1. Congruent Triangles

2. You identified and used congruent triangles.
After
Before
You identified and used congruent triangles.
You will name and use congruent parts of congruent triangles and prove triangles are congruent using the definition of congruence.

3. Check: Which of the following Set of Shapes Congruent?

4. Congruent shapes have the exact same shape and size.
Sometimes the shapes are rotated.

5. Definition of Congruent Polygons
Two polygons are congruent if and only if their corresponding parts (angles and sides) are congruent.

6. CPCTC
If two polygons are congruent then their corresponding parts are congruent.
For triangles we call this Corresponding Parts of Congruent Triangles are Congruent.

7. Example using CPCTC
In the diagram, △ABC ≅△FDE. Find the values of x and y.

8. Solution ∠B≅∠D Therefore, y = 48° ∠A≅∠F ∠A = 180 - (108 + 48)
= = 24
Therefore 2x - y = 24
2x - 48 = 24
2x =
2x = 72
2x/2 = 72/2
x = 36

9. Another Example

10. Third Angles Theorem
If two angles of one triangle are congruent to two angles and a second triangle, then the third angles of triangles are congruent.

11. Example 2: Prove Third Angles Theorem
When the video stops for a while attempt the proof before you finish the video.

12. Assignment
4-3 Study Guide and Intervention
First page