1. Lesson 4-2
Congruent
Triangles

2. Congruent Figures Common English
Congruent figures are two figures that have the same size and shape.
IF two figures are congruent THEN they have the same size and shape.
IF two figures have the same size and shape THEN they are congruent.
Two figures have the same size and shape IFF they are congruent.
Precise Math / Logic

3. Does this pair appear to be congruent?

4. Congruent Triangles
Two triangles are congruent IFF their vertices can be matched up so that the corresponding parts (angles and sides) of the triangle are congruent.

5. Congruent Triangles
Two triangles are congruent IFF their vertices can be matched up so that the corresponding parts (angles and sides) of the triangle are congruent.
ABC  RST
1. A  R
2. B  S
3. C  T
4. AB  RS
5. BC  ST
6. CA  TR A R
iff C B T S

6. Congruent Triangles
Two triangles are congruent IFF their vertices can be matched up so that the corresponding parts (angles and sides) of the triangle are congruent.
ABC  RST
1. A  R
2. B  S
3. C  T
4. AB  RS
5. BC  ST
6. CA  TR A S T
iff C B R

7. Watch Carefully !!!!! ABC  ABC A A 1. A  A 2. B  B 3. C  C
4. AB  AB
5. BC  BC
6. CA  CA
Because C C B B
ABC  ABC

8. But . . . ABC  ACB A A 1. A  A 2. B  C 3. C  B 4. AB  AC
5. CB  BC
6. CA  BA
Because C B C B
ABC  ACB

9. SUN  RAY Also NUS  YAR Also USN  ARY
When referring to congruent triangles (or polygons), we must name corresponding vertices in the same order. R S U N R A Y Y A U N
SUN  RAY
Also NUS  YAR S
Also USN  ARY

10. How would you write that these two figures are congruent?
Write your answer on a piece of paper. P O U M N E A T S
Pentagon MONTA  Pentagon PERSU
Pentagon ATNOM  Pentagon USREP
Etc. R