The angle formula is divided into tangent formula and complementary angle formula, the tangent formula is expressed by tan, and the complementary angle formula is expressed by cos. Tangent formula: k=(y2-y 1)/(x2-x 1), cosine formula: k=(y2-y 1)/(x2-x 1).

Inversetangent function is a mathematical term, one of the inverse trigonometric functions, which refers to the inverse function of function y=tanx.

The inverse function of the tangent function y=tanx in the open interval (x∈(-π/2, π/2)) is denoted as y=arctanx or y=tan- 1x, which is called the arc tangent function. It represents the only fixed angle on (-π/2, π/2) whose tangent is equal to x, that is, tan(arctanx)=x, and the domain of the arctangent function is r, that is, (-∞, +∞). The arctangent function is an inverse trigonometric function.