In this page we practice using the idea that:

Two exterior angles at the same vertex are equal.

Example 1

One exterior angle = 100°

Find the other exterior angle.

Answer:

The second exterior angle = 100°

Example 2

One exterior angle = 75°

Find the other exterior angle.

Answer:

The second exterior angle = 75°

Example 3

One exterior angle = x
The other exterior angle = 2x − 30

Since they are equal:

x = 2x − 30

x = 30°

Example 4

One exterior angle = 3x
The other exterior angle = x + 40

Since they are equal:

3x = x + 40

2x = 40

x = 20°

Practice

• More Examples

• Take the Quiz

Continue Learning

1. Types of Triangles
2. Triangles (Basics)
3. Sum of Angles of a Triangle is 180° (Proof)
4. Find the Missing Angle of a Triangle
5. Sum of Exterior Angles of a Triangle (Proof)
6. Exterior Angle Theorem of a Triangle
7. Two Exterior Angles at a Vertex are Equal (Proof)
8. Two Exterior Angles are Equal at a Vertex (Quick Proof)

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