Two or more angles are supplementary if their sum is 180. An angle is twice the size of its supplement. Set up and solve an equation to find the measures of the two angles.

Step-by-step explanation:

Let "a" represent the measure of the angle. Then 180-a is the measure of its supplement. Your equation can be ...

  a = 2(180-a) . . . an equation

  a = 360 -2a . . . . eliminate parentheses

  3a = 360 . . . . . . add 2a

  a = 120 . . . . . . . . divide by 3 to find "an angle"

  180-a = 60 . . . . . find "its supplement"

The measure of the angle is 120°, of its supplement, 60°.