Curriculum for Grade 3
Students' strong foundation of math skills facilitates the shift to multiplication and division, moving from concrete procedures toward abstract thinking and automaticity.
MODULE 1. Properties of Multiplication and Division and Solving Problems with Units of 2-5 and 10
Topic A: Multiplication and the Meaning of the Factors
Students build upon their knowledge of addition to identify factors (how many groups, how many objects in each group) and to compose and solve simple multiplication equations. They work with groups of 2-5 identical objects, beginning with models of identical concrete objects, such as bunches of bananas and fingers on a hand. As students progress, they work with more abstract objects (identical beads) and objects in an array.
Solve and re-write repeated addition equations
Complete statements describing equal groups and their totals
Use the multiplication sign
Express multiplication equations based on a model
Solve and express multiplication equations based on a model
Compose and solve multiplication equations based on a model
Multiply based on a model of objects in rows
Compose and solve multiplication equations based on an array
Compose expressions and equations based on a model
Topic B: Division as an Unknown Factor Problem
Students work with models of real-world objects to solve equal sharing problems. They are introduced to the division symbol. They use the "dealing" method to create groups of a given size. Based on these models, they answer the questions, "How many groups?" and "How many in each group?" They compose and solve division equations.
Use the division symbol
Compose and solve division equations based on a model
Model division equations and solve
Divide objects into groups
Compose division equations
Solve division word problems
Topic C: Analyzing Arrays to Multiply Using Units of 2 and 3
Students deepen and expand their understanding of multiplication by 2 and 3 with new ways of visualizing the concept. The topic focuses on skip counting and arrays which helps students begin to see patterns as they multiply and solve equations. Students also discover and explore the commutative and distributive properties of multiplication.
Skip count by 2 (Level 1)
Skip count by 3 (Level 1)
Multiply by 2 with and without an array model (Level 1)
Multiply by 3 with and without an array model (Level 1)
Multiply by 2 to complete a pattern of equations (Level 1)
Multiply by 3 to complete a pattern of equations (Level 1)
Label arrays with equations to show the commutative property of multiplication by 2
Label arrays with equations to show the commutative property of multiplication by 3
Complete equations to show the commutative property of multiplication by 2 (Level 1)
Complete equations to show the commutative property of multiplication by 3 (Level 1)
Solve x2 multiplication equations (Level 1, Part 1)
Solve x3 multiplication equations (Level 1, Part 1)
Solve x2 multiplication equations (Level 1, Part 2)
Solve x3 multiplication equations (Level 1, Part 2)
Skip count by 2 (Level 2)
Skip count by 3 (Level 2)
Multiply by 2 with and without an array model (Level 2)
Multiply by 3 with and without an array model (Level 2)
Multiply by 2 to complete a pattern of equations (Level 2)
Multiply by 3 to complete a pattern of equations (Level 2)
Complete equations to show the commutative property of multiplication by 2 (Level 2)
Complete equations to show the commutative property of multiplication by 3 (Level 2)
Label arrays with equations to show the distributive property of multiplication by 2 (Part 1)
Label arrays with equations to show the distributive property of multiplication by 2 (Part 2)
Label arrays with equations to show the distributive property of multiplication by 3 (Part 1)
Label arrays with equations to show the distributive property of multiplication by 2 (Part 3)
Label arrays with equations to show the distributive property of multiplication by 3 (Part 2)
Solve x2 multiplication equations (Level 2, Part 1)
Solve x3 multiplication equations (Level 2, Part 1)
Solve x2 multiplication equations (Level 2, Part 2)
Solve x3 multiplication equations (Level 2, Part 2)
Topic D: Division by 2 and by 3
Students use concrete and abstract objects to understand the concept of division. They then relate division to multiplication to help build understanding and fact fluency. Students begin by solving simple division equations (quotients to 5) and then advance to solving equations with quotients to 10.
Distribute objects equally to create a tape diagram (How many in each group?)
Represent a tape diagram as a division equation (How many in each group?)
Distribute objects equally to create a tape diagram (How many groups?)
Represent a tape diagram as a division equation (How many groups?)
Complete equations to relate multiplication to division (Part 1)
Complete equations to relate multiplication to division (Part 2)
Match a division fact to its related multiplication fact
Solve division equations by using the related multiplication fact
Solve division equations with a divisor of 2 (Level 1)
Solve division equations with a divisor of 3 (Level 1)
Solve division equations with a divisor of 2 or 3
Solve division equations with a divisor of 2 (Level 2)
Solve division equations with a divisor of 2 (Level 3)
Solve division equations with a divisor of 3 (Level 2)
Solve division equations with a divisor of 3 (Level 3)
Topic E: Multiplication and Division by 4
Building upon previous learning about multiplication and division, students apply their understanding to facts using 4 as a product or divisor. They work with familiar manipulatives and progression of skills to build understanding and fluency.
Skip count by 4
Multiply by 4 with and without an array model
Multiply by 4 to complete a pattern of equations
Solve x4 multiplication equations
Represent a tape diagram as a multiplication equation (Level 1)
Represent a tape diagram as a multiplication equation (Level 2)
Label a tape diagram to represent a multiplication equation
Identify factors and product in a multiplication equation
Label arrays with equations to show the commutative property of multiplication (Level 1)
Label arrays with equations to show the commutative property of multiplication (Level 2)
Label tape diagrams with equations to show the commutative property of multiplication
Solve multiplication equations based on the commutative property
Solve word problems using tape diagrams and multiplication equations
Solve division equations by using the related multiplication fact
Solve division equations with a divisor of 4 (Level 1)
Solve division equations with a divisor of 4 (Level 2)
Topic F: Multiplication and Division by 5
Building upon previous learning about multiplication and division, students apply their understanding to facts using 5 as a product or divisor and 10 as a product. They also develop understanding of the distributive property of multiplication and division. Students build connections between equations, arrays, tape diagrams, and word problems.
Skip count by 5
Multiply by 5 with and without an array model
Multiply by 5 to complete a pattern of equations
Solve x5 multiplication equations
Solve division equations by using the related multiplication fact
Solve division equations with a divisor of 5 (Level 1)
Solve division equations with a divisor of 5 (Level 2)
Label arrays with equations to show the distributive property of multiplication
Complete expressions based on the distributive property of multiplication
Compose a division equation based on an array
Compose a division equation based on an array to show the distributive property of division
Solve a division equation based on an array by using the distributive property of division
Complete expressions based on the distributive property of division
Skip count by 10
Multiply by 10 to complete a pattern of equations (Level 1)
Multiply by 10 to complete a pattern of equations (Level 2)
Solve x10 multiplication equations
Solve word problems using tape diagrams and division equations (Level 1)
Solve word problems using tape diagrams and division equations (Level 2)
MODULE 2. Place Value and Problem Solving with Units of Measure
Topic A: Time Measurement and Problem Solving
Students review telling time on an analog clock and learn to write time as hours and minutes. They also learn how to use addition and subtraction skills to calculate start and end times and time intervals and apply this to word problems.
Review telling time to five minutes
Tell time to the minute (Level 1)
Tell time to the minute (Level 2)
Identify the start and end times of a scenario
Calculate the time interval
Calculate time intervals using a timeline
Calculate time intervals, without a timeline
Rewrite time as hr and min
Calculate the end time using addition
Calculate the end time using column addition (Level 1)
Calculate the end time using column addition (Level 2)
Calculate the end time using column addition (Level 3)
Calculate the start time using subtraction
Calculate the start time using column subtraction (Level 1)
Calculate the start time using column subtraction (Level 2)
Find the time a certain number of minutes earlier than a given time
Calculate the start time when the end time and time intervals are known (Level 1)
Calculate start time when the end time and time interval are known (Level 2)
Topic B: Measuring Weight and Liquid Volume in Metric Units
Students use a scale and a pan balance with weights to determine the mass of objects. They learn to read a scale between labeled increments and to add and subtract mass measurements to solve problems. To learn how to measure capacity, students pour liquid into labeled containers. They learn the relationship between kilograms and grams and between liters and milliliters.
Measure the mass of objects in kilograms using a scale
Measure the mass of objects in kilograms using a pan balance
Measure the mass of objects in grams using a pan balance
Compare grams and kilograms
Tutorial: Drag the lace to match objects
Match the estimated mass in grams and kilograms to objects
Determine mass measurements on a scale that is only labeled in increments of 10
Add or subtract to compare or find the total mass of objects measured on a scale
Tutorial: Click on highlighted words to access definition
Determine visually which of two objects has a greater capacity
Measure capacity using non-standard units and liters
Measure capacity in liters
Measure capacity in milliliters
Learn about the relationship between liters and milliliters, and compare the two units of measure
Compare measures in liters and milliliters to determine which is greater or if they are equal
Measure capacity in milliliters
Topic C: Rounding to the Nearest Ten and Hundred
Using a number line to provide context, students first determine the midway point between two round numbers. They then progress to rounding using the number line and the midway point. Finally, students round 2-, and 3-digit numbers to any given place value.
Identify numbers in the tens, hundreds, or thousands place
Identify the neighboring tens of a given number on a number line
Discover the concept of rounding
Round to the nearest ten using a number line and learn about the approximation symbol
Use the approximation symbol when rounding to the nearest ten using a number line for reference
Round to the nearest ten and learn the language "round up" or "round down."
Round to the nearest ten using the language "round up" or "round down."
Learn the rule for rounding numbers that are exactly in the middle of two tens
Round a given number to the nearest ten (Part 1)
Round a given number to the nearest ten using the rule for rounding
Round a given number to the nearest ten (Part 2)
Determine the neighboring hundreds of a given number on a number line
Identify the neighboring hundreds of a given number and round to the nearest hundred
Learn the rule for rounding numbers that are exactly in the middle of two hundreds
Determine whether a given number rounds up or down to the nearest hundred
Round a given number to the nearest hundred using the rule for rounding
Round a given number up or down to the nearest hundred
Round a given number up or down to the nearest ten and hundred
Round a given number up or down to the nearest ten or hundred (Level 1)
Round a given number up or down to the nearest ten or hundred (Level 2)
Topic D: Two- and Three-Digit Measurement Addition Using the Standard Algorithm
Students review the standard algorithm for addition with regrouping and then use it to solve word problems involving measurements. As they progress, they receive fewer prompts to complete the standard algorithm.
Add 2-digit numbers using the standard algorithm with regrouping
Add 2-digit numbers using the standard algorithm with regrouping to solve word problems
Add 3-digit numbers using the standard algorithm with regrouping (Level 1)
Add 3-digit numbers using the standard algorithm with regrouping (Level 2)
Add 3-digit numbers using the standard algorithm with regrouping to solve word problems (Level 1)
Add 3-digit numbers using the standard algorithm with regrouping to solve word problems (Level 2)
Add 3-digit numbers using the standard algorithm with regrouping (Level 3)
Add 3-digit numbers using the standard algorithm with regrouping to solve word problems (Level 3)
Topic E: Two- and Three-Digit Measurement Subtraction Using the Standard Algorithm
Students review the standard algorithm for subtraction with regrouping and then use it to solve word problems involving measurements. As they progress, they receive fewer prompts to complete the standard algorithm.
Subtract 2-digit numbers using the standard algorithm with regrouping
Subtract 2-digit numbers using the standard algorithm with regrouping to solve word problems
Subtract 3-digit numbers using the standard algorithm with regrouping (Level 1)
Subtract 3-digit numbers using the standard algorithm with regrouping (Level 2)
Subtract 3-digit numbers using the standard algorithm with regrouping to solve word problems (Level 1)
Subtract 3-digit numbers using the standard algorithm with regrouping (Level 3)
Subtract 3-digit numbers using the standard algorithm with regrouping (Level 4)
Subtract 3-digit numbers using the standard algorithm with regrouping to solve word problems (Level 2)
MODULE 3. Multiplication and Division with Units of 0, 1, 6-9, and Multiples of 10
Topic A: The Properties of Multiplication and Division
Students enrich their understanding of multiplication and division by introducing the multiplication chart and the commutative property (or 'turnaround facts') of multiplication. They continue to build fact fluency, adding factors 6-9 to their repertoire.
Illustrate the commutative property by labeling arrays and tape diagrams
Solve equations that illustrate the commutative property
Determine missing products in a multiplication chart (factors to 5)
Determine missing products in a multiplication chart (one factor > 5)
Skip count by 6
Determine multiples of 6 in a multiplication chart
Skip count by 7
Determine multiples of 7 in a multiplication chart
Skip count by 8
Determine multiples of 8 in a multiplication chart
Skip count by 9
Determine multiples of 9 in a multiplication chart
Determine missing products in a multiplication chart (one factor > 5)
Solve for an unknown represented by a letter in multiplication equations
Solve for an unknown represented by a letter in division equations
Match an equation containing an unknown to a statement
Solve for an unknown represented by a letter in multiplication and division equations
Compose and solve a multiplication equation based on a tape diagram
Solve a multiplication word problem using a tape diagram
Topic B: Multiplication and Division Using Units of 6 and 7
Students begin with familiar tasks taken to a more challenging level with higher factors. They deepen their understanding of the relationship between multiplication and division as well as their fact fluency.
Skip count by 6
Determine multiples of 6 in a multiplication chart
Determine products of 6 in a times table with and without an array model
Determine products of 6 in a times table
Solve division problems with a divisor of 6 based on its relationship to multiplication
Solve division problems with a divisor of 6 (Level 1)
Solve division problems with a divisor of 6 (Level 2)
Skip count by 7
Determine multiples of 7 in a multiplication chart
Determine products of 7 in a times table with and without an array model
Determine products of 7 in a times table
Solve division problems with a divisor of 7 based on its relationship to multiplication
Solve division problems with a divisor of 7 (Level 1)
Solve division problems with a divisor of 7 (Level 2)
Solve multiplication equations using the break apart and distribute strategy
Solve for an unknown represented by a letter in multiplication equations
Solve for an unknown represented by a letter in division equations
Solve a word problem using a tape diagram and the relationship between multiplication and division
Topic C: Multiplication and Division Using Units up to 8
In addition to extending students' mastery of multiplication and division to include 8, they are also introduced to multi-step equations that use parentheses. Using illustrations and step-by-step instruction, students learn that parentheses and order of operations do not affect multiplication-only equations. They also continue to build their mastery of the break apart and distribute strategy.
Skip count by 8
Determine multiples of 8 in a multiplication chart
Determine products of 8 in a times table with and without an array model
Determine products of 8 in a times table
Solve division problems with a divisor of 8 based on its relationship to multiplication
Solve division problems with a divisor of 8 (Level 1)
Solve division problems with a divisor of 8 (Level 2)
Solve multi-step equations that include parentheses (Level 1)
Compare similar multi-step equations with parentheses in different places
Solve multi-step equations that include parentheses (Level 2)
Identify a multi-step equation with parentheses that is solved correctly
Recognize the effect of parentheses on multi-step multiplication equations (Part 1)
Recognize the effect of parentheses on multi-step multiplication equations (Part 2)
Re-group factors with parentheses as a strategy to solve multi-step multiplication equations (Part 1)
Re-group factors with parentheses as a strategy to solve multi-step multiplication equations (Part 2)
Solve multiplication equations using the break apart and distribute strategy (Part 1)
Solve multiplication equations using the break apart and distribute strategy (Part 2)
Solve division equations using the break apart and distribute strategy (Part 1)
Solve division equations using the break apart and distribute strategy (Part 2)
Topic D: Multiplication and Division Using Units of 9
Students apply and extend previous understanding to include 9 as a factor or divisor. We also introduce a strategy specifically for multiplying by 9.
Skip count by 9
Determine multiples of 9 in a multiplication chart
Determine products of 9 in a times table with and without an array model
Determine products of 9 in a times table
Solve division problems with a divisor of 9 based on its relationship to multiplication
Solve division problems with a divisor of 9 (Level 1)
Solve division problems with a divisor of 9 (Level 2)
Solve multiplication equations using the break apart and distribute strategy
Solve multiplication equations using the 9 = 10-1 strategy
Topic E: Analysis of Patterns and Problem Solving Including Units of 0 and 1
Students dig deeper into concepts of multiplication and division as they work with 1 and 0. In addition to working with these numbers as factors, dividends, and divisors, students use a letter to represent an unknown number in an equation and are introduced to let statements regarding such letters.
Compose a multiplication sentence (including 1 x n) to represent a mode
Solve multiplication problems that use 1 as a factor (including 1 x n)
Solve division problems that use 1 as a divisor (including n / 1)
Compose a multiplication sentence (including n x 1) to represent a model
Solve multiplication problems that use 1 as a factor (including n x 1)
Solve division problems in which a number is divided by itself
Solve for an unknown (represented by a letter) in multiplication and division problems that include 1
Compose a multiplication sentence (including n x 0) to represent a model
Solve multiplication problems that use 0 as a factor (including n x 0 and 0 x n)
Solve division problems that use 0 as a dividend (including 0 / n)
Solve for an unknown (represented by a letter) in multiplication and division problems that include 0
Determine whether a multiplication or division equation with an unknown represented by a letter is true based on a let statement
Topic F: Multiplication of Single-Digit Factors and Multiples of 10
Building upon students' fact fluency with single-digit factors, we introduce multiplying a single-digit factor by a multiple of ten. Students relate word-based multiplication (e.g., 4 x 3 tens = 12 tens) to numeric equations (e.g., 4 x 30 = 120).
Solve for missing products on a multiplication chart in which 10 is a factor
Relate a product of n tens to the product as a number n0
Match numeric products to multiplication equations that use numbers and words (n tens)
Use properties of multiplication to simplify and solve equations
Solve multiplication equations that have a single digit and a multiple of ten as factors
Solve for missing products on a multiplication chart that are square numbers
MODULE 4. Multiplication and Area
Topic A: Foundations for Understanding Area
Students are introduced to the very basics of area using tiling. They learn to use square units, measure sides of a rectangle, skip count rows of tiles, and rearrange tiles to form a different rectangle with the same area.
Identify 2-dimensional shapes
Tile 2-dimensional shapes to compare their area
Determine and compare area by tiling with square units
Identify shapes that have a given area
Determine area by tiling with square centimeters or inches
Determine area of a rectangle made by rearranging tiles from another rectangle
Determine area by skip counting tiles in each row
Topic B: Concepts of Area Measurement
Building upon the previous module, students start by skip counting tiles in a rectangle to determine its area. They then progress to multiplication using a tiled rectangle and one with only labeled measurements. Students rearrange tiles to determine the measurements of a different rectangle that has the same area. They also solve for an unknown side represented by a letter.
Tutorial: Click on the book to see the multiplication table
Multiply to find the area of a tiled rectangle (Level 1)
Multiply to find the area of a tiled rectangle (Level 2)
Determine the area of a rectangle by multiplying the lengths of the sides (Level 1)
Determine the area of a rectangle by multiplying the lengths of the sides (Level 2)
Determine the area of a rectangle based on the equal area of a different rectangle
Determine the length of a side based on the area of a rectangle
Topic C: Arithmetic Properties Using Area Models
Students dig deeper into their understanding of multiplication and area by using area models of rectangles. They compare parts to the whole, find missing parts, and manipulate equations to demonstrate properties. Exercises begin by using rectangles with gridlines and then advance to using those without.
Multiply to find area by splitting a rectangle into smaller parts
Use the distributive property of multiplication to find the area of a rectangle split into smaller parts
Subtract to find the area of a covered part of a rectangle
Multiply or subtract to find areas of rectangles without gridlines
Topic D: Applications of Area Using Side Lengths of Figures
Students learn two different approaches to finding the area of a composite shape based on side lengths. In the first, they break the shape into smaller rectangles and add those areas together. In the second, they "complete" the shape to find the total area and then subtract the area of the "missing piece". Students begin by using shapes with unit squares shown and then progress to those without.
Determine area of a composite shape by splitting it into two rectangles and adding the areas (Part 1)
Determine area of a composite shape by completing the rectangle and subtracting the area of the missing piece (Part 1)
Determine area of a composite shape by completing the rectangle and subtracting the area of the missing piece (Part 2)
Determine area of a composite shape by splitting it into two rectangles and adding the areas (Part 2)
Determine the area of a composite shape using either the "break apart and add" or "complete and subtract" strategy
MODULE 5. Fractions as Numbers on the Number Line
Topic A: Partition a Whole into Equal Parts
Students establish a foundation for understanding fractions by working with equal parts of a whole. They use halves, thirds, fourths, fifths, sixths, sevenths, and eighths of shapes including circles, rectangles, line segments, and other shapes. Students partition shapes, label sections, shade fractions, and even solve word problems involving equal sharing. Throughout the topic, they do not use fraction notation (e.g., 2 thirds).
Identify shapes that are partitioned into equal parts
Identify and label halves, fourths, and eighths
Identify and label thirds, fifths, sixths, and sevenths
Determine the number of equal parts needed to partition a shape into a given denominator
Identify the shaded portion of a shape as a unit fraction
Sort shapes based on the unit fraction shaded
Identify the shaded portion of a shape
Identify shapes that have a given portion shaded
Partition and shade a shape to represent a given portion
Solve word problems involving equal parts of a whole
Topic B: Unit Fractions and their Relation to the Whole
Students build upon their knowledge from Topic 5A to transition from word form to standard form in identifying fractions. They begin with unit fractions and advance to more complex fractions, including complements of a whole and improper fractions. Throughout the topic, students are presented with a variety of shapes, sizes, and colors of figures. While they do not use the term "improper fractions," they learn the underlying concept of fractional parts that form more than one whole.
Identify unit fractions written in standard form
Label part of a figure with a unit fraction written in standard form
Identify the part of a figure that is shaded with a unit fraction
Identify figures that have a given unit fraction shaded
Write a unit fraction to identify the shaded part of a figure
Identify the shaded part of a figure
Label the shaded part of a figure with a fraction written in standard form
Shade parts of a figure to represent a given fraction
Identify figures that have a given fraction shaded and fractions that represent the shaded part of a figure
Write a fraction to identify the shaded part of a figure (Level 1)
Label the shaded part of a figure with a fraction written in standard form and word form
Write a fraction to identify the shaded part of a figure (Level 2)
Label shaded and unshaded parts of a figure (Level 1)
Label shaded and unshaded parts of a figure (Level 2)
Solve word problems involving complementary fractions
Determine the number of fractional parts in a whole
Solve problems involving multiple wholes and improper fractions
Identify a set of figures whose shading represents an improper fraction
Label a set of figures whose shading represents an improper fraction
Divide and shade a set of figures to represent an improper fraction
Topic C: Comparing Unit Fractions and Specifying the Whole
Based on visual models, students learn that the more parts in a whole, the smaller each unit fraction. They then compare unit fractions using both words and symbols, and they relate the unit fraction to the whole.
Compare unit fractions based on a model
Compare unit fractions using <, =, and > with and without a model
Identify and label a unit fraction model that is greater or less than a given unit fraction model
Identify a whole based on a given unit fraction
Build a whole using the correct number of unit fraction tiles
Topic D: Fractions on the Number Line
Students apply their understanding of fractions to numbers on a number line. They learn that there are numbers between the whole numbers on a number line and how to identify them. Using this tool, students are able to name equivalent whole number/fraction pairs, label fractions greater than 1, and compare fractions with unlike denominators.
Identify fractions on a number line and write 1 as a fraction
Label fraction numerators on a number line
Label fractions on a number line (numerator and denominator)
Segment a number line into fractions and place a given fraction on the number line
Place a given fraction on a number line visually (without hashmarks)
Label fraction numerators on a number line in numbers greater than 1
Identify a fraction that is equivalent to a whole number on a number line
Place fractions greater than 1 on a number line
Segment a number line into fractions and place a given fraction (greater than 1) on the number line
Label fractions greater than 1 on a number line
Compare fractions with unlike denominators on a number line
Use <, =, or > to compare fractions with unlike denominators on a number line
Topic E: Equivalent Fractions
Using familiar shaded models and the number line, students focus on concepts of equivalent fractions. They extend this understanding to include whole numbers and fractions greater than 1.
Create, label, identify, and compare equivalent fractions
Identify equivalent fractions using the number line (less than 1)
Identify equivalent fractions using the number line (greater than 1)
Label equivalent fractions on a number line
Label two equivalent fractions based on models
Label three equivalent fractions based on models
Label fractions equivalent to 1 whole
Write whole numbers as fractions (denominator of 1)
Write whole numbers as fractions (various denominators)
Topic F: Comparison, Order, and Size of Fractions
Based on visual models, students learn to compare two fractions with the same numerator or two fractions with the same denominator. To do so, they apply their understanding of creating and naming fractions, as well as using the <, =, and > symbols.
Compare fractions with the same numerator or the same denominator based on a model
Shade and compare fractions with the same numerator based on a model
Label and compare fractions with the same numerator
Compare fractions with the same numerator or the same denominator
MODULE 6. Geometry and Measurement Word Problems
Topic A: Problem Solving with Perimeter
Students find the perimeter of a polygon by adding the lengths of its sides. They solve for the length of an unknown side and find the perimeters of equal-sided polygons.