ABSTRACT
The formulae stated above may be used to derive two further compound angle formulae:
tan(A + B) = tan A + tan B 1 − tan A tan B
tan(A − B) = tan A − tan B 1 + tan A tan B
The compound angle formulae are true for all values of A and B, and by substituting values of A and B into the formulae they may be shown to be true.
