1. Warm Up 5-1 Classify each angle as acute, obtuse, or right. 1. 2. 3. 3.
4. If the perimeter is 47, find x and the lengths of the three sides.

2. Classify triangles by their angle measures and side lengths.
5-1
Learning Objectives
Classify triangles by their angle measures and side lengths.
Use triangle classification to find angle measures and side lengths.

3. 5-1
A triangle ( ) is a polygon with three sides. Triangles can be classified in two ways:
(1) by angle measures
(2) or by side lengths.

4. Acute triangle Scalene Equiangular Isosceles Right Equilateral Obtuse
5-1
By angle measure By side length
Acute triangle Scalene
Equiangular Isosceles
Right Equilateral
Obtuse

5. Acute Triangle Three acute angles Triangle Classification
5-1
Triangle Classification
By Angle Measures
Acute Triangle
Three acute angles

6. Three congruent acute angles
5-1
Triangle Classification
By Angle Measures
Equiangular Triangle
Three congruent acute angles

7. Right Triangle One right angle Triangle Classification
5-1
Triangle Classification
By Angle Measures
Right Triangle
One right angle

8. Obtuse Triangle One obtuse angle Triangle Classification
5-1
Triangle Classification
By Angle Measures
Obtuse Triangle
One obtuse angle

9. Example 1A: Classifying Triangles by Angle Measures
5-1
Example 1A: Classifying Triangles by Angle Measures 1 2 3 4

10. Equilateral Triangle Three congruent sides Triangle Classification
5-1
Triangle Classification
By Side Lengths
Equilateral Triangle
Three congruent sides

11. At least two congruent sides
5-1
Triangle Classification
By Side Lengths
Isosceles Triangle
At least two congruent sides

12. Scalene Triangle No congruent sides Triangle Classification
5-1
Triangle Classification
By Side Lengths
Scalene Triangle
No congruent sides

13. Example 1B: Classifying Triangles by Side length
5-1
Example 1B: Classifying Triangles by Side length 2) 1) 3)

14. How to classify triangles in a coordinate plane?
5-1
How to classify triangles in a coordinate plane?
1. Find the coordinates.
2. Use the distance formula to find the length.
3. Compare the length of each side of the triangle.
“I DO”
“You do w/partner”
“You alone”

15. Summary about triangles
5-1
Summary about triangles

16. 5-1
Angles!
Triangles have interior angles and exterior angles.

17. 5-1
Angles!
The sum of interior angles

18. Find the measure of x and classify the triangles
5-1
Find the measure of x and classify the triangles
“I DO” 1

19. Find the measure of x and classify the triangles
5-1
Find the measure of x and classify the triangles
“We do” 2

20. Find the measure of x and classify the triangles
5-1
Find the measure of x and classify the triangles
“You w/partner” 3

21. Find the measure of x and classify the triangles
5-1
Find the measure of x and classify the triangles
“You alone” 4

22. Exterior Angle Theorem
5-1
Exterior Angle Theorem

23. Exterior Angle Theorem Examples
5-1
Exterior Angle Theorem Examples
“I DO” 1

24. Exterior Angle Theorem Examples
5-1
Exterior Angle Theorem Examples
“We Do” 2

25. Exterior Angle Theorem Examples
5-1
Exterior Angle Theorem Examples
“You with a Partner” 3

26. Exterior Angle Theorem Examples
5-1
Exterior Angle Theorem Examples
“You Alone” 3