Remember that when two angles are vertical angles, their angle measurements are the same, as the angles are congruent.
Note the Vertical Angle Theorem. Angles vertically opposite (directly opposite) when two lines intersect are congruent with each other.
Now note that supplementary means 180°
Set the equation. Let the angles = x
2x = 180
Isolate the x. Note the equal sign. What you do to one side, you do to the other. Divide 2 from both sides
(2x)/2 = (180)/2
x = 180/2
x = 90
90° is the measurement of each angle.
~Rise Above the Ordinary
