sin3a=sin(2a+a)=sin2acosa+cos2asina
=2sinacos^2a+cos^2asina-sin^3a
=3sinacos^2a-sin^3a
=3sina(1-sin^2a)-sin^3a
=3sina-4sin^3a
cos3a=cos(2b+b)
=cos2bcosb-sin2bsinb
=cos^3b-cosbsin^2b-2sin^2bcosb
=cos^3b-3cosbsin^2b
=cos^3b-3cosb(1-cos^2b)
=4cos^3b-3cos