** Definition of Base Angle Theorem **

- Base Angle Theorem states that if two sides in a triangle are congruent, then the angles opposite to these sides are also congruent.

**More about Base Angle Theorem **

- Base angles of an isosceles triangle are equal.
- Converse of the base angle theorem is also true, i.e. if two angles of a triangle are congruent, the sides opposite to these angles are congruent.

**Example on Base Angle Theorem**

- In the given triangle, as the sides AB and AC are congruent, the angles opposite to these sides (∠B and ∠C) are also congruent.

**Solved Example on Base Angle Theorem**

The length of two congruent sides of a triangle is 6 cm. Which of the following could be the measure of the three angles of the triangle?

Choices:

A. 108°, 36°, 36°

B. 30°, 90°, 60°

C. 40°, 62°, 78°

D. 42°, 64°, 74°

Correct Answer: A

Solution:

Step 1:According to the base angle theorem, if two sides of a triangle are congruent, the angles opposite to these sides are also congruent.

Step 2:The length of the two sides of the triangle are congruent, so the angles opposite to these sides would be congruent.

Step 3:So, 108°, 36°, and 36° would be the measures of the three angles of the triangle.

**Related Terms for Base Angle Theorem**

- Angle
- Base
- Congruent
- Congruent angles
- Congruent Triangles
- Isosceles Triangle
- Side
- Triangle