CPM Homework Help : CCG Problem 5-9

Multiple Choice: In the triangle below, $x$ must be:

A triangle with a 42 degree angle between two equal sides. Angle x is opposite one of the equal sides.

Hint:

The triangle is isosceles meaning $2$ sides are equal.

More Help:

The measure of $x$ must be the same as the other unknown angle because base angles are equal in an isosceles triangle.

Answer:

Since the sum of all the interior angles of a triangle must be $180º$ , then $x+x+42º=180º$ .
So the answer is B.