1. Section 4.1 Classifying Triangles
Geometry
Section 4.1
Classifying Triangles

2. Triangle – 3-sided polygon named using its 3 vertices
Triangles are classified in two ways: sides and angles.

3. Angle Classifications
All triangles have at least 2 acute angles, the third is used to classify the angle.
Acute triangle - 3 acute angles
Equiangular triangle –
3 congruent acute angles
Obtuse triangle - 1 obtuse angle
Right triangle - 1 right angle

4. Example 1
Classify each triangle as acute, equiangular, obtuse, or right. A.
101° C. B.
60°
40°
60°
60° D.
90°
70°
70°

5. Side Classifications
Triangles are also classified by the number of congruent sides they have.
Equilateral triangle - 3 congruent sides
Isosceles triangle – at least 2 congruent sides
Scalene triangle – no congruent sides

6. Example 2 Classify each triangle equilateral, isosceles, or scalene.
60°
8 in
8 in
60°
60°
10 ft
6 ft
8 ft
4 in

7. Isosceles Triangles
Leg
Leg
Base

8. Example 3
Find the measures of the 3 sides of isosceles triangle KLM with base KL. M
4x - 13
12 - x K L
x + 6

9. Homework
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