BASE ANGLE THEOREM
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.
Video Examples: How to use Base Angles Theorem
Example on Base Angle Theorem
(?B and ?C) are also congruent.
Solved Example on Base Angle Theorem
Ques: 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. 108o, 36o, 36o
B. 30o, 90o, 60o
C. 40o, 62o, 78o
D. 42o, 64o, 74o
Correct Answer: A
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, 108o, 36o, and 36o would be the measures of the three angles of the triangle.