1. Warm Up
Find the measures of the sides of ∆ABC and classify the triangle by its sides.
A(-7, 9) B(-7, -1) C(4, -1)
AB = 10
BC = 11
AC = √221
The triangle is scalene.

2. FG, GH, FH, F, G, H Warm Up 1. Name all sides and angles of ∆FGH.
2. What is true about K and L? Why?
3. What does it mean for two segments to be congruent?
FG, GH, FH, F, G, H
 ;Third s Thm.
They have the same length.

3. Congruent Triangles
Section 4-3

4. Congruent Triangles Same size. Same shape.
All 6 corresponding parts (angles and sides) of two triangles are congruent.
CPCTC: “Corresponding parts of congruent triangles are congruent.
Example: If ∆ABC  ∆DEF, then…

5. Example: Naming Congruent Corresponding Parts
Given: ∆PQR  ∆STW
Identify all pairs of corresponding congruent parts.
Angles: P  S, Q  T, R  W
Sides: PQ  ST, QR  TW, PR  SW

6. Example: Using Corresponding Parts of Congruent Triangles
Given: ∆ABC  ∆DBC.
Find the value of x.
x = 53

7. Example: Given: ∆ABC  ∆DEF Find the value of x. Find mF. x = 4

8. Triangle Congruence Theorem
Congruence of triangles is:
Reflexive
Symmetric
Transitive

9. Congruence Transformations
To slide (translate), flip (reflect), or turn (rotate) triangles does not change their size or shape.
∆ABC → ∆A'B'C'

10. Example: Proving Triangles Congruent
Given: YWX and YWZ are right angles.
YW bisects XYZ. W is the midpoint of XZ. XY  YZ.
Prove: ∆XYW  ∆ZYW

11. Statements
Reasons
1. YWX and YWZ are rt. s.
1. Given
2. YWX  YWZ
2. All Rt.  are 
3. YW bisects XYZ
3. Given
4. XYW  ZYW
4. Def. of bisector
5. W is mdpt. of XZ
5. Given
6. XW  ZW
6. Def. of mdpt.
7. Reflex. Prop. of 
7. YW  YW
8. X  Z
8. Third s Thm.
9. XY  YZ
9. Given
10. ∆XYW  ∆ZYW
10. Def. of  ∆

12. Lesson Quiz
1. ∆ABC  ∆JKL and AB = 2x JK = 4x – 50. Find x and AB.
Given that polygon MNOP  polygon QRST, identify the congruent corresponding part.
2. NO  ____ T  ____
31, 74 RS P