Trigonometry is a subarea of geometry that covers triangles. The angles and the length of sides are important for calculation of right-angled triangle. The longest side of a right triangle is across from the right angle and is called a hypotenuse. The other two (shorter) sides are the legs of the right triangle. The side that is referred to as the adjacent leg is adjacent to the calculated angle, and the opposite leg is opposite from the calculated angle. You can use the angle functions to calculate the legs and hypotenuse of a right triangle based on the angles. With the arc functions, you can calculate the angles based on the legs and hypotenuse. The angle functions are explained by using a full circle (360 degrees) that allows for all angle possibilities.