Wow, lol. Never thought of doing it that way. Here's how I did it:
Sin3a = Sin(2a+a)
=Sin2aCosa+Cos2aSina
=(2SinaCosa)Cosa+(1-2Sin²a)Sina
=2SinaCos²a +Sina - 2Sin³a
=2Sina(1-Sin²a) + Sina - 2Sin³a
=2Sina -2Sin³a + Sina - 2Sin³a
=3Sina - 4Sin³a.
edit - Oh. ^^;;