Tim C. answered • 01/17/17

Experienced and Effective Specialist in Praxis Math and GED Math

The three angles of any triangle always add up to be 180.

So if x, y, and z are the three angles, then x + y + z = 180.

If z is the third angle, then z = 180 - x - y.

Another way to look at this is that you start with 180 and you subtract away the two angles you know, x and y, which leaves you an amount for the third angle.