A

right triangle is a that has one . The side opposite the right is always the longest and is known as the

hypotenuse. The other sides are commonly called

legs. Notice that in a right triangle, the legs are to each other.

If one of the in the triangle is labeled, the legs can be discussed relative to that angle. Consider an acute angle labeled as

$∠θ$ on the diagram. The side that forms the angle is the

adjacent side and the side not touching the angle is the

opposite side.

Note that the opposite and adjacent sides change when

$∠θ$ changes, but the hypotenuse is always the same.