Section 10–4 Perimeters & Areas of Similar Figures. Objectives: 1) To find perimeters & areas of similar figures. Reminder of Perimeter & Area. Perimeter – Distance around a figure Perimeter of any polygon - add up the lengths of all of the sides
1) To find perimeters & areas of similar figures.
ΔABC ~ ΔFDE
Side ratio =
Perimeter Ratio = Side Ratio
Perimeter Ratio = 5/4
Area Ratio = a2/b2 =
The ratio of the lengths of the corresponding sides of 2 regular octagons is 8/3. The area of the larger octagon is 320ft2. Find the area of the smaller octagon.
Side ratio =
Now, set up an area proportion using the area ratio!
Area ratio =
x = 45ft2
The areas of 2 similar pentagons are 32in2 and 72in2. What is their similarity (side) ratio? What is the ratio of their perimeter.
Remember: Side ratio is a/b and area ratio is a2/b2. So if the area ratio is given, you must take the square root of the numerator and the denominator.
Side Ratio and the Perimeter ratio
The similarity (side) ratio of two similar Δis 5:3. The perimeter of the smaller Δ is 36cm, and its area is 18cm2. Find the perimeter & area of the larger Δ.
Write the side ratio and then find the perimeter.
Write the area ratio and then find the area.
PL = 60cm
A = 50cm2