Cos (x-y)
------------ =
Cos (x+y)
1 + tanx tany
--------------
1 - tanx tany
and
Sin 3x=3sinx-4sin^3x
Any help would be greatly appreciated
sin 3x = sin( 2x +x )
= sin2xcosx + sinxcos2x
= (2sinxcosx)cosx + (cos^2x - sin^2x)sinx
= 2sinxcosx^2 + cos^2xsinx - sin^3x
= ...