Lesson 8-5

For Examples 1-3 Use Area Formulas for Polygons
Find the are of each figure.

a. Find the area of a rectangle with length 14 feet and width 9 feet.

A = ℓw		Area of a rectangle
A = 14 ∙ 9	Replace ℓ with 14 and w with 9.	
A = 126	Multiply.

The area is 126 square feet.

b. Find the area of a square with side length 5 inches.

5 in.

5 in.

A = s2		Area of a square
A = 52		Replace s with 5.
A = 25		Multiply.

The area is 25 square inches.

c. [Real-World Example] BEDROOMS   The Jones family is moving into a new house. Blake’s new bedroom is rectangular in shape with length 14 feet and width 12 feet. What is the area of Blake’s new bedroom?

The length is 14 feet, and the width is 12 feet.

A = ℓw		Area of a rectangle
A = 14 ∙ 12	Replace ℓ with 14 and w with 12.
A = 168	Multiply.

The area of Blake’s new bedroom is 168 square feet.

d. Find the area of the parallelogram.

The base is 
3 units, and the height is 6 units.

A = bh	Area of parallelogram	
A = 3  6	Replace b with 3 and h with 6.
A = 18		Multiply.	

The area is 18 square units or 18 units2.

e. Find the area of the parallelogram.

	Estimate A ≈ 15 ∙ 10 or 150 in2

A = bh	Area of parallelogram	
A = 15  9	Replace b with 15 and h with 9.
A = 135	Multiply.		

The area is 135 square inches or 135 in2.

Check for Reasonableness Compare 135 with the estimate. 135 ≈ 150 

f. Find the area of the triangle.

By counting, you find that the measure of the base is 4 units and the height is 4 units.

A = 	Area of a triangle	
A = 	Replace b with 4 and h with 4.
A = 	Simplify the numerator.
A = 8	Divide.

The area of the triangle is 8 square units.	

g. Find the area of the triangle.

A = 		Area of a triangle	
A = 		Replace b with 6.4 and h with 9.5.
A = 		Simplify the numerator.
A = 30.4		Divide.				

The area of the triangle is 30.4 square centimeters.