Question

3 points

The measure of the vertex angle of an isosceles triangle is 120 degrees. What is the measure of the base angle?
O 30 degrees
0 40 degrees
O 35 degrees
O 60 degrees

Answer 1

a) The measure of the base angle is 30°.

Explanation:

The angle formed by the vertex of two equal sides in an isosceles triangle is called a VERTEX ANGLE.

Also, the other two base angles are equals they are opposite to equal sides.

Now, let us assume that the base angle = a

So, by ANGLE SUM PROPERTY:

Sum of all angles of triangle = 180°

⇒ 120° + a + a = 180°

or, 2 a = 180 -120 = 60°

or, a = 60/2 = 30°

or, a = 30°

Hence, the measure of the base angle is 30°.