1. 4.3 Warm Up
Are the triangles similar? If so, which theorem justifies your answer.

2. 4.3 Theorems about Proportions
SWBAT use the Triangle Proportionality theorem and the Triangle Mid-segment theorem to solve for missing sides of triangles.

3. Angle Bisector and Proportional Side Theorem
When an interior angle of a triangle is bisected, 2 similar triangles are formed.
A bisector of an angle in a triangle divides the opposite side into 2 segments whose lengths are the same ratio as the length of the adjacent to the angle If
AB = BD
AC DC
Then

4. 24 = 8
30 DB
24DB = 240
24DB = 240
DB = 10

5. If DE II BC,
Then AD = AE
DB EC

6. Example

7. If L1 II L2 II L3,
Then AB = DE
BC EF

8. Example

9. If the midsegment JG is parallel to DS, then JG = DS 25 10
If the midsegment JG is parallel to DS, then JG = DS 2