Question 400653
Expanding the left side, we get


{{{sin^2(a) + 2sin(a)cos(a) + cos^2(a)}}} Since {{{sin^2(a) + cos^2(a) = 1}}}, and {{{2sin(a)cos(a) = sin(2a)}}}, the expression is equivalent to


{{{1 + sin(2a)}}}, and we're done.