Tan sum angle formula Tan (α-β) = (tan α-tan β)/(1+tan α tan β). The addition theorem of sum angle formula, also called trigonometric function, is the relationship between the sum (difference) trigonometric function of several angles and the trigonometric function of each angle. Trigonometric function is a kind of transcendental function in elementary function in mathematics.

Formulas, in mathematics, physics, chemistry, biology and other natural sciences, use mathematical symbols to express the relationship between several quantities. It is universal and applicable to all similar problems. In mathematical logic, a formula is a formal grammatical object to express a proposition, but the proposition may depend on the free variable value of the formula. The precise definition of a formula depends on the specific formal logic involved, but there is a very typical definition (for first-order logic): the formula is defined relative to a specific language; That is, a set of constant symbols, function symbols and relational symbols, in which each function and relational symbol has an arity to indicate the number of parameters it accepts.