1. 4.2 Congruence and Triangles
Two geometric figures are congruent if they have exactly the same size and shape.
When two figures are congruentcorresponding angles are congruent and corresponding sides are congruent.

2. ABC =̃ PQR B Q A P R C

3. Third Angles Theorem
If two angles of one triangle are congruent to two angles of another triangle, then the third angles are also congruent.

4. Properties of Congruent Triangles
Reflexive Property: Every triangle is congruent to itself.
Symmetric Property of Congruent Triangles: If ABC =̃ DEF, then DEF =̃ ABC
Transitive Property of Congruent Triangles:
If ABC =̃ DEF and DEF =̃ JKL, then ABC =̃ JKL.

5. Practice Problems Name the congruent figures
Given M =̃ G and N =̃ H, find the value of x. E B D
ABC=̃ EFD A C F
(2X-50)° H M
142° N J
24° P G
X=32

6. More Practice Problems
Given that N =̃ R and L =̃ S, find the value of x. L M N
55°
65° T S R
(2X+30)°
X=15

7. Given that LMN =̃ PQR, answer the following: mP= QR =̃ mM= LN =̃
mR=
mN= N R L P M Q
45°
105°
105° MN PR
45°
30°
30°

8. Identify any figures that can be proved congruent
Identify any figures that can be proved congruent. If congruent, write a congruence statement. B A C D