Question

At ∆ ABC, the exterior angle at C, measures 126 °. If the ∡B measures twice the ∡A. How long is ∡A?

Answer 1

42°

Explanation:

An exterior angle is equal to the sum of the opposite interior angles.

A + B = 126

The measure of B is twice the measure of A.

B = 2A

Substitute:

A + 2A = 126

3A = 126

A = 42

Answer 2

<A=42°

Explanation:

If the exterior of angle C is 126, the interior is 54.

The sum of the other two angles must be 126. (Exterior Angle Theorem)

If B is twice A, we divide 126 into thirds. This is 42.

So A is 42, B is 84, and C is 54.