prove that sin^6a+sin^4acos ^2a-sin^ 2acos^4a=1-2cos^2a

Answer 1

Clearly the equation is wrong. If a = π/4, we have

sina = cosa = 1/√2 and the equation is

1/8 + 1/8 - 1/8 = 1 - 2(1/2)

which is false.