1. Classifying Triangles
Geometry

2. First we will learn to classify by the
ANGLES

3. Right triangles have ONE right angle

4. Acute Triangles have three acute angles Acute Angle Smaller than 90o

5. Obtuse Triangles have
ONE obtuse angle
Obtuse Angle

6. We will now learn to classify triangles by their sides.

7. Equilateral Triangles have
3 equal sides

8. Isosceles Triangles have
2 equal sides.

9. Scalene Triangles have
NO equal sides.

10. Let’s Review: Classifying Triangles by Their Sides
EQUILATERAL – 3 congruent sides
ISOSCELES – at least two sides
congruent
SCALENE – no sides congruent
EQUILATERAL
ISOSCELES
SCALENE

11. Let’s Review: Classifying Triangles by Their Angles
EQUIANGULAR – all angles are congruent
ACUTE – all angles are acute
RIGHT – one right angle
OBTUSE – one obtuse angle
EQUIANGULAR
ACUTE
RIGHT
OBTUSE

12. A Challenge: Classify the Triangles!
∆ABE
∆BFC
∆FCE
∆CDE
∆BCE

13. You have now learned that triangles can be classified by either their sides or their angles.

14. NOW!!! Look back at each of the types of triangles and see if you can identify a relationship between the side length and the size of its opposite angle.