Question

In an isosceles triangle if the angle at the vertex measures 70 degrees, then what is the measure of base angles?

• A. 45 degrees
• B. 55 degrees
• C. 65 degrees
• D. 35 degrees

Answer 1

The correct option is B

55 degrees

In an isosceles triangle, the base angles are equal. Let the base angles be 'x'
Using the property of sum of angles in a triangle we can write,

x + x + 70 = 180 [Sum of angles of a triangle is 180 degrees]

i.e. 2x + 70 = 180

2x = 180 - 70 = 110

2x = 110

Solving for x we get, x = 55

So each base angle of a given isosceles triangle is 55 degrees.