Tan[z] gives the tangent of z.
Mathematical function (see Section A.3.10).
The argument of Tan is assumed to be in radians. (Multiply by Degree to convert from degrees.)
Sin[z]/Cos[z] is automatically converted to Tan[z]. TrigFactorList[expr] does decomposition.
Tan is automatically evaluated when its argument is a simple rational multiple of ; for more complicated rational multiples, FunctionExpand can sometimes be used.
See The Mathematica Book: Section 1.1.3 and Section 3.2.6.
See also: ArcTan, Cot, TrigToExp, TrigExpand.