sin(x+y)=sinxcosy+cosxsiny
sin(x-y)=sinxcosy-cosxsiny
cos(x+y)=cosxcosy-sinxsiny
cos(x-y)=cosxcosy+sinxsiny
sin2x=2sinxcosx
cos2x=cosxcox-sinxsinx
sinx+siny=2sin((x+y)/2)cos((x-y)/2)
sinx-siny=2sin((x-y)/2)cos((x+y)/2)
cosx+cosy=2cos((x+y)/2)cos((x-y)/2)
cosx-cosy=-2sin((x+y)/2)sin((x-y)/2)
sin(-x)=-sinx
cos(-x)=cosx
tg(-x)=-tgx
ctg(-x)=-ctgx
