If two lines intersect and one of the angles formed from the intersection is 90°, what is the measurement of the adjacent angle?
It's your lucky day, because you've got two options here. Yes, that's right: there are two ways to figure this problem out.
First, we know that if two lines intersect, one angle and its adjacent angle will add up to 180° because they form a straight angle together. If one is 90°, the other is 180° – 90° = 90°. No, that's not a crazy coincidence. Why? Because of our second option.
When two lines form a 90° angle, they're perpendicular. Perpendicular lines actually form four 90° angles, not just one. So the adjacent angle to a 90° angle will be a 90° angle also. Shocker.