The TAN function returns the tangent of an angle provided in radians. In geometric terms, the tangent of an angle returns the ratio of a right-triangle's opposite side over its adjacent side. For example, the the tangent of PI()/4 (45°) returns the ratio of 1.0.
The graph of the tangent function, shown above, visualizes the output of the function for angles from 0 to a full rotation corresponding to the range [0, 2π]. The function has two vertical asymptotes within the range [0, 2π] where the output diverges to infinity. The tangent function can be equivalently defined in terms of SIN and COS: