Given an integer, how do you find it's opposite?

Which property is illustrated by the following statement? if hxa rgi, then rgi hxa.

He that is measured at 220° is a reflex angle. the opposite angle is obtuse. find the measure of obtuse .

The radius of the circle below intersects the unit circle at (3/5,4/5). what is the approximate value of theta? 0.6 radians 1.0 radians 36.9 degrees 53.1 degrees