1. Classifying Triangles
Notes 3.6
Classifying Triangles

2. Triangles C A B AB, BC, and AC are the sides of ABC.
A, B, C are the triangle's vertices.

3. Classifying Triangles
BY THEIR ANGLES

4. Acute Triangle
All 3 angles are acute (less than 90).

5. Equiangular Triangle All 3 angles are the same (60).
If all angles are equal then all sides must be equal too.

6. Right Triangle
One right angle.

7. Obtuse Triangle
One obtuse angle.

8. Example 1A: Classifying Triangles by Angle Measures
Classify BDC by its angle measures.
B is an obtuse angle.
B is an obtuse angle. So BDC is an obtuse triangle.

9. Classifying Triangles
BY THEIR SIDES

10. Equilateral Triangle 3 congruent sides
If all sides are equal then all angles must be equal too.

11. Isosceles triangle Has at least 2 congruent sides
Vertex Angle
Leg
Leg
Base
Base Angle
Base Angle
Has at least 2 congruent sides
Base angles are always congruent

12. Scalene Triangle
No congruent sides

13. Example 2A: Classifying Triangles by Side Lengths
Classify EHF by its side lengths.
Isosceles.

14. Lesson Summary Classify each triangle by its angles and sides.
∆ MNQ
∆ NQP
∆ MNP
4. Find the side lengths of the triangle.
acute; equilateral
obtuse; scalene
acute; scalene
29; 29; 23