Perimeter and Area Ratios for Similar Polygons

2.6 Perimeters and Areas of Similar Figures

NOTES: TB pg 76-79, WB pg 41-42
HW: WB pg 44

Key Idea 1: When two figures are similar, the ratio of their perimeters is equal to the ratio of their corresponding

side lengths.

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⭐️ Goal: Find ratios of similar figures

example 1, Perimeter

In your notebook...

The height of Figure A is 9 feet. The height of a similar Figure B is

15 feet. What is the ratio of the perimeter of A to the perimeter of B?

Multiple Choice

The two figures are similar. Find the ratios (red to blue) of the perimeters

• 14:9

• 18:28

• 196:81

Key Idea 2: When two figures are similar, the ratio of their areas is equal to the square of the ratio of their corresponding side lengths.

​

⭐️ Goal: Find ratios of similar figures

example 2, AREA

In your notebook...

The base of Triangle P is 8 meters. The base of a similar Triangle Q is 7 meters. What is the ratio of the area of P to the area of Q?

Multiple Choice

The two figures are similar. Find the ratios (red to blue) of the area

• 14:9

• 18:28

• 196:81

Find Perimeter & Area with Ratios

A swimming pool is similar in shape to a volleyball court. Find the perimeter P and the area A of the pool.

Steps: Set up a proportion for perimeter, use key idea 1, solve for the pool's perimeter. Next, set up a proportion for the area, use key ideas 2 to find the pool's area.