Area is a measure of the space inside a 2D object.

How can you find the area of a rectangle?

I can measure the sides of the rectangle, and then find the area using the formula length times width.

[Show students a composite shape made up of multiple rectangles]. How can you find the area of this shape?

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.

Can you break rectangles into other shapes?

I can draw lines to break a rectangle into other rectangles, squares, triangles, and other polygons.

If you break a rectangle into other shapes, what is the total area of all of the shapes?

The total area of all of the shapes is equal to the area of the original rectangle.

How is the area of a right triangle related to the area of a rectangle?

The area of a right triangle is half the area of a rectangle with the same base and height.

How is the area of a parallelogram related to the area of a rectangle?

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.

How can you find the area of a polygon?

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.

How do you plot points on a coordinate plane to make a polygon?

First I plot each point. The coordinates tell me the position of the point on the x-axis and the y-axis. 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.

How does finding the area of a polygon on a coordinate grid compare to finding the area of a polygon drawn off of a grid?

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.

Area of Polygons (Using Decomposition)

LESSON MATERIALS move

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What you will learn from this videoWhat you will learn

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 Video
  What is area?ANSWER
  - Area is a measure of the space inside a 2D object.
  How can you find the area of a rectangle?ANSWER
  - I can measure the sides of the rectangle, and then find the area using the formula length times width.
  [Show students a composite shape made up of multiple rectangles]. How can you find the area of this shape?ANSWER
  - 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.
  Can you break rectangles into other shapes?ANSWER
  - I can draw lines to break a rectangle into other rectangles, squares, triangles, and other polygons.
  If you break a rectangle into other shapes, what is the total area of all of the shapes?ANSWER
  - The total area of all of the shapes is equal to the area of the original rectangle.
- After Video
  How 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.
  How is the area of a parallelogram related to the area of a rectangle?ANSWER
  - 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.
  How can you find the area of a polygon?ANSWER
  - 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.
  How do you plot points on a coordinate plane to make a polygon?ANSWER
  - First I plot each point. The coordinates tell me the position of the point on the x-axis and the y-axis. 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.
  How does finding the area of a polygon on a coordinate grid compare to finding the area of a polygon drawn off of a grid?ANSWER
  - 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
- Decompose (a shape) DEFINE
- Polygon DEFINE
- Rectangle DEFINE
- Triangle DEFINE
- Right triangle DEFINE
- Parallelogram DEFINE
- Kite DEFINE
- Trapezoid DEFINE
Reading Material
Practice Word Problems
Practice Number Problems
Lesson Plan
Teacher Guide
Assessment
Online Quiz Game Quiz PDF Exit Ticket