Post on 31-Dec-2015
description
Geometry
Unit VIIPerimeters and Areas of Similar
Figures
Objective: to compare and solve perimeters and areas of similar figures
two rectangles two right triangles two circles
Scale __________ __________ __________ factor Ratio of __________ __________ __________ perimeters Ratio of __________ __________ __________ the areas
8
6
5
4 10
8
9
6
18
12
๐=54๐ด=162
๐ด=72๐=36
69=
23
3654
=46=
23
72162
=3681
=49
๐2=25+16๐=โ41
๐=9+โ 41๐ด=10
๐2=100+64๐=2โ 41๐=18+2โ41
๐ด=40
12
9+โ 4118+2โ41
1040
=14
(8)
๐ถ=16๐๐ด=64๐
(6)
๐ถ=12๐๐ด=36๐
68=
34
12๐16๐
ยฟ34
36๐64๐
ยฟ9
16
Perimeters of Similar Polygons: Two similar figures with lengths of corresponding sides in the ratio of
a:b will have perimeters in the ratio of a:b.
Theorem 11.5: Areas of similar polygons: Two similar figures with lengths of corresponding sides in the
ratio of a:b will have areas in the ratio of .
Examples: The ratio of corresponding sides in two similar polygons is 3:5. a) Find the ratio of the perimeters. b) Find the ratio of the areas. c) If the perimeter of the first polygon is 36cm, find the perimeter of the second polygon. d) If the second polygon has an area of 80cm2, find the area of the first polygon.
3 :5
9 :25
35=
36๐ฅ 3 ๐ฅ=180 ๐ฅ=60๐๐
925
=๐ฅ
80 25 ๐ฅ=720 ๐ฅ=28.8๐๐2