Question

,prove geometrically that cos (A+B) = cos A Cos B - sin A Sin B and hence prove that cos2A = cos square A - sin square A​

Answer 1

answer:

cos(a+b)=AC−BC=AC−FD

=cos(a)cos(b)−sin(a)sin(b)

sin(a+b)=BF+FE=CA+FE

=sin(a)cos(b)+cos(a)sin(b)