Warm Up Find the area of each figure

Warm Up Find the area of each figure. Give exact answers, using if necessary. 1. a square in which s = 4 m 16 m 2 2. a circle in which r = 2 ft 4 ft 2 3. What’s bigger: two 10 in pizzas or a 20 in pizza? Are they the same?

Lesson 9 -5 Effects of Changing Dimensions

Find the perimeter and area of each rectangle. Compare the larger rectangle to the smaller using division. Rectangle A 2” Rectangle B 4” 3” P= A= 6” P= A=

What if we only change length and leave width alone? Rectangle A: 2 x 4 Rectangle B: 6 X 4 What was the scale factor for the length change? How did this affect the Area?

What if we change length and width but by different factors? Rectangle A: 2 x 4 Rectangle B: 6 x 8 Length change factor: Width change factor: Area change:

Is this true for all shapes or just rectangles? Consider circles Circle A: r = 3 Circle B: r = 9 Scale Factor for radius? Area change?

What about Squares? Square A: s=4 Scale factor? Area change? Square B: s = 12

When the dimensions of a figure are changed proportionally, the figure will be similar to the original figure.

Example 3 A: Effects of Changing Area A circle has a circumference of 32 in. If the area is multiplied by 4, what happens to the radius? Helpful Hint

Example 3 B: Effects of Changing Area An equilateral triangle has a perimeter of 21 m. If the area is multiplied by the side length? , what happens to

Summary The relationship between perimeter and area of similar figures is as follows: • If you know the change in perimeter, the area is changed by that number squared. • If you know the change in area you can square root to find the change in perimeter. Homework: p 625 1 -7, 30 -32, 41, 42 Quiz tomorrow! Test on Thursday!