The number 2A can be written as ((A+B)+(A−B)).
tan2A=tan((A+B)+(A−B))
=tan(A+B)+tan(A−B)1−tan(A+B)tan(A−B)
=x+y1−xy
The number 2B can be written as ((A+B)−(A−B)).
tan2B=tan((A+B)−(A−B))
=tan(A+B)−tan(A−B)1+tan(A+B)tan(A−B)
=x−y1+xy
Find the value of tan 3A in terms of tanA & tan2A