1. Determine whether the triangles are similar. Justify your answer.
A. yes, SSS Similarity
B. yes, ASA Similarity
C. yes, AA Similarity
D. No, sides are not proportional.
5-Minute Check 1

2. Concept

3. A. In the figure, DE and EF are midsegments of ΔABC. Find AB.
Use the Triangle Midsegment Theorem
A. In the figure, DE and EF are midsegments of ΔABC. Find AB.
Example 3

4. ED = AB Triangle Midsegment Theorem 1 2 5 = AB Substitution 1 2
Use the Triangle Midsegment Theorem
ED = AB Triangle Midsegment Theorem __ 1 2
5 = AB Substitution __ 1 2
10 = AB Multiply each side by 2.
Answer: AB = 10
Example 3

5. B. In the figure, DE and EF are midsegments of ΔABC. Find FE.
Use the Triangle Midsegment Theorem
B. In the figure, DE and EF are midsegments of ΔABC. Find FE.
Example 3

6. FE = BC Triangle Midsegment Theorem
Use the Triangle Midsegment Theorem __ 1 2
FE = BC Triangle Midsegment Theorem
FE = (18) Substitution __ 1 2
FE = 9 Simplify.
Answer: FE = 9
Example 3

7. C. In the figure, DE and EF are midsegments of ΔABC. Find mAFE.
Use the Triangle Midsegment Theorem
C. In the figure, DE and EF are midsegments of ΔABC. Find mAFE.
Example 3

8. By the Triangle Midsegment Theorem, AB || ED.
Use the Triangle Midsegment Theorem
By the Triangle Midsegment Theorem, AB || ED.
AFE  FED Alternate Interior Angles Theorem
mAFE = mFED Definition of congruence
mAFE = 87 Substitution
Answer: mAFE = 87
Example 3

9. A. In the figure, DE and DF are midsegments of ΔABC. Find BC.
Example 3

10. B. In the figure, DE and DF are midsegments of ΔABC. Find DE.
Example 3

11. C. In the figure, DE and DF are midsegments of ΔABC. Find mAFD.
Example 3