As you proceed through your physics studies, you will find it necessary to understand the Pythagorean theorem, which is reviewed in this section. At the right, you see a right triangle (a triangle with a 90° angle). The Pythagorean theorem states that the square of the hypotenuse (the side opposite the right angle) equals the sum of the squares of the two legs. This equation is shown in Equation 1 to the right.

There are two specific right triangles that occur frequently in physics homework problems. In an isosceles right triangle, the two legs are the same length and the hypotenuse is the length of either leg times the square root of two. The angles of an isosceles right triangle are 45, 45 and 90 degrees, so it is also called a 45-45-90 triangle.

When the angles of the triangle measure 30, 60 and 90 degrees, it is called a 30-60-90 triangle. The shorter leg, the one opposite the 30° angle, is one half the length of the hypotenuse. This relationship makes for an easy mathematical calculation and makes this triangle a favorite in homework problems.