Enjoy any 5 free lessons!
You can pick. No account needed.
Watch VideoYou have remaining on your free trial.
4 Free Lessons Left
Get unlimited access to all videos and lesson plans with a membership.
So you can keep watching more great videos in class, ask your teacher or principal to get a School plan membership.
Become a member to get full access to our entire library of learning videos, reading material, quiz games, simple DIY activities & more.
Become a member to get full access to our entire library of learning videos, quiz games, & more.
Plans & Pricingto watch this full video.
Access All Videos
and Lessons, No Limits.
Access All Videos
No credit card required,
takes 7 sec to signup.
No card required
Readytogo lessons
that save you time.
Readytogo lessons
If you are on a school computer or network, ask your tech person to whitelist these URLs:
*.wistia.com, fast.wistia.com, fast.wistia.net, embedwistiaa.akamaihd.net
Sometimes a simple refresh solves this issue. If you need further help, contact us.
Area of Polygons (Using Decomposition)
 Show lesson plan & teacher guide
 Show answers to discussion questions
 Show video only
 Allow visiting of other pages
 Hide assessments
 We'll learn to find the area of polygons by decomposing shapes.
 We will also learn how to find the area of polygons displayed on a coordinate plane.
 And we will see how this knowledge helps people create video games, build houses and even skateboard ramps!

Discussion Questions
 Before VideoWhat is area?ANSWER
Area is a measure of the space inside a 2D object.
I can measure the sides of the rectangle, and then find the area using the formula length times width.
I can break the shape into two rectangles. I can find the area of each rectangle and add the areas together to find the area of the bigger shape.
I can draw lines to break a rectangle into other rectangles, squares, triangles, and other polygons.
The total area of all of the shapes is equal to the area of the original rectangle.
 After VideoHow is the area of a right triangle related to the area of a rectangle?ANSWER
The area of a right triangle is half the area of a rectangle with the same base and height.
I can break a parallelogram into two identical right triangles and a rectangle. When I combine the two triangles it forms a new rectangle. The area of this set of shapes is the same as the area of a rectangle with a length and width the same as the length and height of the parallelogram.
I can divide a polygon into rectangles and right triangles. Then I can find the area of each of the smaller shapes and add them together to find the total area.
First I plot each point. The coordinates tell me the position of the point on the xaxis and the yaxis. After I plot each point, I connect the points to make a polygon. I need to connect the points with straight lines and make a closed shape.
I can find the area in the same way, by dividing the shape into rectangles and triangles and finding the total area of those shapes.

Vocabulary
 Area DEFINE
The measure of the space enclosed by the sides of a shape.
 Decompose (a shape) DEFINE
Breaking a shape into smaller shapes.
 Polygon DEFINE
A closed shape with straight sides.
 Rectangle DEFINE
A closed shape with 4 straight sides with 4 right angles.
 Triangle DEFINE
A closed shape with 3 straight sides.
 Right triangle DEFINE
A triangle where one angle measures 90 degrees.
 Parallelogram DEFINE
A closed shape with 4 straight sides. Two pairs of sides are parallel.
 Kite DEFINE
A closed shape with 4 straight sides. Two pairs of adjacent (next to each other) sides have the same length.
 Trapezoid DEFINE
A closed shape with 4 straight sides. At least one pair of sides are parallel.
 Area DEFINE

Reading Material

Practice Word Problems

Practice Number Problems

Lesson Plan

Teacher Guide