So becomes , in which we can rearrange the terms (because we can add two numbers in any order). So turns into which was the original left hand side of the given equation.
To answer the question, recall that = cot(x) and = tan(x).
Therefore,
+ = cot(x) + tan(x) = ( commutativity of the addition operation ) = tan(x) + cot(x) = (as it is given) = . ANSWER