Similar Figures

1
7-6
Similar Figures
Warm Up
Problem of the Day
Lesson Presentation
Pre-Algebra
2
Warm Up Solve each proportion.
1.
b 10
y 8
2.
m 52
3.
4.
p 3
3
Learn to determine whether figures are similar,
to use scale factors, and to find missing
dimensions in similar figures.
4
The heights of letters in newspapers and on
billboards are measured using points and picas.
There are 12 points in 1 pica and 6 picas in one
inch.
A letter 36 inches tall on a billboard would be
216 picas, or 2592 points. The first letter in
this paragraph is 12 points.
5
A picture 10 in. tall and 14 in. wide is to be
scaled to 1.5 in. tall to be displayed on a Web
page. How wide should the picture be on the Web
page for the two pictures to be similar?
The picture should be 2.1 in. wide.
6
A T-shirt design includes an isosceles triangle
with side lengths 4.5 in, 4.5 in., and 6 in. An
advertisement shows an enlarged version of the
triangle with two sides that are each 3 ft. long.
What is the length of the third side of the
triangle in the advertisement?
The third side of the triangle is 4 ft long.
7
Congruent figures have the same size and shape.
Similar figures have the same shape, but not
necessarily the same size. The As in the table
are similar. The have the same shape, but they
are not the same size.
The ratio formed by the corresponding sides is
the scale factor.
8
Remember!
The following are matching, or
corresponding ?A and ?X
A
X
Y
Z
C
B
?B and ?Y
?C and ?Z
9
Which rectangles are similar?
Since the three figures are all rectangles, all
the angles are right angles, the corresponding
angles are congruent.
J and K ?
J and L ?
K and L ?
10
Are the triangles similar?
5 ft
30
7 ft
45
12 ft
6 ft
No, the corresponding angles are not congruent.
11
Are the parallelograms similar?
12 in
12 in
10 in
8 in
12
The figures below are similar. Solve for x
12 cm
10 cm
x cm
4 cm
13
Homework

• Pg 370
• 1 9 all, 11 14 all, 21 26 all