A right triangle is a triangle with one right angle (one angle equal to 90°).

The side opposite the right angle (the longest side) is called the hypotenuse.

The remaining two sides (the sides that intersect to determine the right angle) are called the legs of the right triangle.

Once a reference angle (other than the right angle) has been chosen, one of the legs of the triangle can be referred to as being opposite the reference angle, while the other can be referred to as being adjacent to the reference angle.

Sometimes it is required to solve a right triangle to find unknown lengths of sides or unknown measures of angles.