In this page we practice finding missing angles using the rule:
Sum of interior angles = 180°
Example 1
A = 60°
B = x
C = 30°
60 + x + 30 = 180
x = 90°
Example 2
A = x
B = 90°
C = 40°
x + 90 + 40 = 180
x + 130 = 180
x = 50°
Example 3
A = 50°
B = 100°
C = x
50 + 100 + x = 180
150 + x = 180
x = 30°
Example 4
A = x
B = 60°
C = x
x + 60 + x = 180
2x + 60 = 180
2x = 120
x = 60°
Example 5
D = x
E = 90°
F = x − 20°
x + 90 + (x − 20) = 180
2x + 70 = 180
2x = 110
x = 55°
Example 6
G = x
H = 3x
I = 2x
x + 3x + 2x = 180
6x = 180
x = 30°
Practice
- More Examples
Continue Learning
- Types of Triangles
- Triangles (Basics)
- Sum of Angles of a Triangle is 180° (Proof)
- Find the Missing Angle of a Triangle
- Sum of Exterior Angles of a Triangle (Proof)
- Exterior Angle Theorem of a Triangle
- Two Exterior Angles at a Vertex are Equal (Proof)
- Two Exterior Angles are Equal at a Vertex (Quick Proof)