Question 408715
{{{sin(a+b) - sin(a-b) = sin(a)cos(b) + sin(b)cos(a) - (sin(a)cos(b) - sin(b)cos(a))}}}. The {{{sin(a)cos(b)}}} terms cancel out, so our expression is equal to {{{sin(b)cos(a) - (-sin(b)cos(a)) = 2sin(b)cos(a)}}} which is the RHS, so we're done.