prove sin(3a)cos(a)-cos(3a)sin(a)=2sin(a)cos(a)
sin(3a)cos(a)-cos(3a)sin(a) = 2sin(a)cos(a)
Use the identity that (sinAcosB - sinBcosA) = sin (A - B)
sin (3a - a ) =
sin(2a) = 2sin(a)cos(a)
