cos(α+β)= cosαcosβ-sinαsinβ； Cos(α-β)=cosαcosβ+sinαsinβ. The addition theorem of sum angle formula is also called trigonometric function, which is the relationship between the sum (difference) trigonometric function of several angles and the trigonometric function value of each angle. Trigonometric function is a kind of transcendental function in elementary function in mathematics.

Usage: The sum angle formula is a basic formula of trigonometric function. In fact, there are the following aspects: 1, the derivation basis of other trigonometric functions, 2, the calculation of trigonometric functions, and 3, the calculation of trigonometric functions. Pythagorean theorem can calculate the function value corresponding to each angle, which is the basic tool for compiling trigonometric function table.