Tan inverse is the function used to determine an angle when given the ratio between the length of the side opposite the angle over the length of the side adjacent to the angle. It is sometimes indicated by the terms "arctan" and "atan."
The inverse tangent function is written as "tan" followed by the number negative one in superscript. The inverse sine and the inverse cosine functions operate in the same way as inverse tangent, using the ratio between two sides of a triangle to determine a given angle. The ratio can be used for the angle calculated by the function, and all angles positive or negative 360 degrees.