Question

If in a triangle abc, a=6, b=3 and cos(a-b)=4/5, then its area is

Answer 1

cos(A-B)=4/5

therefore, 1-tan2(A-B)/2 = 4/5

1+tan2(A-B)/2

By componendo dividendo,

2tan2(A-B) = 5-4

2 5+4