I am not quite sure how to prove this, I can see it involves using a double angle formula (see http://mathworld.wolfram.com/Double-AngleFormulas.html). I have tried working backwards but to no avail. Any ideas? Uploaded with ImageShack.us
Thanks, I managed to do it using [tex] \cos a \sin b = (\sin (a+b) - \sin(a-b))/2 [/tex] PROBLEM SOLVED!