1. Warm Up
Identify each number as rational, irrational or not real and explain why.
-14.5 18
1.6 9
5) …… 6)
7) 6/0
8) 0/4

2. Learn to determine whether figures are similar, to use scale factors, and to find missing dimensions in similar figures.

3. Vocabulary
similar
congruent angles
scale factor

4. Similar figures have the same shape, but not necessarily the same size.
Two figures are similar if the ratios of the lengths of corresponding sides are PROPORTIONAL and the corresponding angles are CONGRUENT. Angles that have equal measures are called congruent angles.
43°
43°

5. To determine if two figures are similar, you must determine
if their sides form equivalent ratios
Either cross multiply, or simplify!

6. Are they similar? Q 10 A 8 5 4 R C S B 3 6

7. Are they similar? Write a similarity statementQ
28° A
52° R C S B

8. Are they similar?

9. The ratio formed by the corresponding sides is the scale factor.

10. To determine what
scale factor
Was used:
New length
Old length

11. If trapezoids ABCD and JKLM are similar, 10
If trapezoids ABCD and JKLM are similar,
what is the scale factor of ABCD to JKLM?

12. What scale factor was applied?
Triangle A
Triangle A’
12 in
4.8 in
18 in
7.2 in

13. What scale factor was applied?
Trapezoid A’
4.76 in
Trapezoid A
3.4 in
5.2 in
7.28 in

14. Use the scale factor or set up a proportion to determine the missing side of a similar figure.

15. Find the value of x if the rectangles are similar:9 12 x 6

16. Find the value of x if the triangles are similar

18. A toy company produces two kites whose shapes are geometrically similar. Determine the length of the missing side of the smaller kite.

19. A blue rectangular tile and a red rectangular tile are similar
A blue rectangular tile and a red rectangular tile are similar. The blue tile has a length of 10 inches and a width of 5 inches. The red tile has a length of 6 inches. What is the perimeter of the red tile?

20. Independent Practice:
Pg 116 #1-5
Homework:
117/118 # 1-11