Question

cos^4 (A/2)- sin^4(A/2)=cosA

Answer 1

Answer:

LHS=cos^4(A/2)-sin^4(A/2)

={cos^2(A/2)}^2 -{sin^2(A/2)}^2

={cos^2(A/2) - sin^2(A/2)}{cos^2(A/2) +sin^2(A/2)}

=cosA×1

=cosA