Question 765624
the sum of the angles in a triangle is 180 degrees.
there are 3 angle in a triangle, 2 of which are equal to each other if the triangle is isosceles.
the vertex angle (at the apex) is equal to 54 degrees.
there are 2 angles left, both of which are equal to each other.
180 - 54 = 126 / 2 = 63 degrees for each of the base angles.
54 + 63 + 63 = 180.