Download 4-4 Using Congruent Triangles: CPCTC

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Chapter 4 - Section 4
Using Congruent Triangles: CPCTC
CPCTC Theorem
Use this to prove parts of congruent triangles are congruent AFTER you have proved the
triangles are congruent.
Example 1:
In an umbrella frame, the stretchers are congruent and they open to angles of equal measure.
Given: SL  SR ,
1  2
Prove: 3  4
You can use congruent triangles and CPCTC to measure distances indirectly.
Example 2:
According to legend, one of Napoleon’s officers used congruent triangles to estimate the width of a river.
On the riverbank, the officer stood up straight and lowered the visor of his cap until the farthest thing he
could see was the edge of the opposite bank. He then turned and noted the spot on his side of the river
that was in line with his eye and the tip of his visor.
Given: DEG and DEF
are right angles
EDG  EDF
Prove: EF  EG
HW: Geometry Worksheet Section 4.4