1. Triangles
Lesson 10-4

2. Triangle
A triangle is a figure that has 3 sides and 3 angles. The sum of the measure of the angles is 180°
m<1 + m<2 + m<3 = 180° 1 2 3

3. Find the missing angle measure
<1 = 50° <2= 75° <3 = ?

4. Find the missing angle measure
<1 = 50° <2= 75° <3 = ?
= 125
180 – 125 = 55°

5. Classify Triangles Using Angles
Acute Triangle
Properties: All acute angles.

6. Classify Triangles Using Angles
Right Triangle
Properties: 1 right angle.

7. Classify Triangles Using Angles
Obtuse Triangle
Properties: 1 obtuse angle.

8. Classify Triangles Using Sides
Scalene Triangle
Properties: No congruent sides.

9. Classify Triangles Using Sides
Isosceles Triangle
Properties: At least 2 congruent sides.
This symbol represents that the sides are congruent.

10. Classify Triangles Using Sides
Equilateral Triangle
Properties: 3 congruent sides.

11. Naming Triangles Triangles have a 2 part name.
The first part of the name, names the angles (acute, obtuse, or right)
The second part of the name, names the sides (scalene, isosceles, or equilateral)
Example: Obtuse Scalene

12. Name the Triangle
Acute Scalene

13. Name the Triangle
Right Scalene

14. Name the Triangle
Acute Equilateral

15. Find the missing angle. Then classify the triangle as acute, right, or obtuse.x
40°

16. Find the missing angle. Then classify the triangle as acute, right, or obtuse.
20°
25° x

17. Find the missing angle. Then classify the triangle as acute, right, or obtuse.
30° x
130°

18. Don’t Forget Class Assignment: Homework: Old Blue p. 588 - Lesson 10-4
Old Blue - read p ; complete p (1-28)
IXL Lesson P7 (minimum 80%)
Homework: Old Blue p Lesson 10-4