Apart gives the partial fraction decomposition of a rational expression.
Apart writes expr as a polynomial in var together with a sum of ratios of polynomials, where the degree in var of each numerator polynomial is less than that of the corresponding denominator polynomial.
Apart[expr, Trig->True] treats trigonometric functions as rational functions of exponentials, and manipulates them accordingly.
Apart automatically threads over lists in expr, as well as equations, inequalities, and logic functions.