Before we study trigonometry, we need to know how the sides of a right triangle are named. The three sides are called hypotenuse, adjacent and opposite sides.
In the following right triangle PQR,
the side PQ, which is opposite to the right angle is called the hypotenuse. (The hypotenuse is the longest side of the right triangle.)
the side RQ is called the adjacent side of angle q .
the side PR is called the opposite side of angle q .