The cosine of zero degrees is equal to one. The cosine is a trigonometric function that can be defined through the Pythagorean Theorem as the length of the side of a right triangle adjacent to an angle over the hypotenuse of the triangle.
The cosine of an angle can be found by calculating the ratio, or by calculating the value using the cosine function on a scientific or graphing calculator. The cosine is related to the trigonometric functions sine and tangent. The cosine function can be used to evaluate angles expressed in either degrees or radians. The inverse of the cosine function is known as arccos.