Question

What is the measure of the vertex angle of an isosceles triangle if one of its base angles measures 54° A) 126 B) 72 C) 63 D) 108

Answer 1

An isosceles triangle has congruent base angles, so if one of the base angles measure 54 degrees, then the other base angle does, too.
And a triangle measures up to 180 degrees.
180 = x + 2(54)
180 = x + 108
x = 72
So the answer is B) 72

Answer 2

An isosceles triangle has same  base angles
 if one of the base angles measure 54 degrees, 2nd is  also 54
And a triangle measures up to 180 degrees.
180 = x + 2(54)
180 = x + 108
x = 72
 B) 72 is right option
hope this helps