1. Lesson 4-R
Chapter 4 Review

2. Objectives
Review Chapter 4

3. Vocabulary
None new

4. Triangle Classification
By Angles
Largest Angle
Acute
< 90
Right
= 90
Obtuse
> 90
By Sides
Number of Equal Sides
Scalene
None; all different
Isosceles
Two
Equilateral
All three
Acute
Isosceles
Acute
Equilateral
(also equiangular)
Obtuse
Scalene

5. Triangle Congruence ∆ABC  ∆LMN
“CPCTC” – corresponding parts of congruent triangles are congruent
Angles match by single letter
Sides match by two letter groups
Order Rules!!!
If proving triangles congruent, always mark only one triangle up with S (for sides) and A (for angles) based on the items you have congruent -- that will make it easier to figure out which theorem or postulate applies

6. Triangle Congruence Theorems
Post/Thrm
Picture
Hidden Features
SSS
Shared Side
SAS
Vertical Angles
// Lines  Alt Int ’s
ASA
AAS S S S S S A A S A A A S

7. Hidden Features in Triangle 
Picture
Triangles  by
Shared Side
SSS
Vertical Angles
SAS
Parallel Sides (lines)
Alternate Interior Angles
AAS S S S S S A A A S

8. Finding the Measures of Angles
Rules for finding measures of angles
Linear Pairs sum to 180
Vertical Angles are equal
Sum of the angles in a Triangle = 180
Exterior angle = sum of remote interiors
Use angle classification to eliminate impossible answers
Corner of paper is a 90° angle

9. Isosceles Triangle Theorems
Angles opposite congruent sides are congruent
Sides opposite congruent angles are congruent

10. Summary & Homework
Summary: 4
Homework:
study for test