Question

Use what you know about triangles to find the measure of the third angle.

Angle A= 78º, B= 45º, C= x

x=?

Responses

49º

57º

61º

54º

Answer 1

x = 57°

Explanation:

Pre-Solving

We are given a triangle, and we know that the angles in the triangle are <A, <B, and <C.

We know that m<A = 78° and m<B=45°. We want to find the measure of angle C, which we know currently as x.

Solving

Recall that all angles in a triangle add up to 180°. This means that m<A + m<B + m<C = 180°.

Substituting what we know into that equation, we get:

78° + 45° + x = 180°

We can add 78 and 45 degrees together.

123° + x = 180°

Subtract 123° from both sides.

x = 57°

So x, or m<C is 57°.