sin^2 x+ cos^2 x=1
2cos^2 x -1=1- 2sin^2 x=cos^2 x-sin^2 x= cos2x
sin2x=2sinxcosx
sin(a+b)=sin(a)cos(b)+cos(a)sin(b)
sin(a-b)=sin(a)cos(b)-cos(a)sin(b)
cos(a+b)=cos(a)cos(b)-sin(a)sin(b)
cos(a-b)=cos(a)cos(b)+sin(a)sin(b)
sin^2 x=(1-cos^2 x)/2
cos^2 x=(1cos^2 x)/2
