Sin(x+y)-cosxsiny Cos(x-y)-sinxsiny Sinacosb-sin(a-b) Cosacosb-cos(a-b)
Sinxcosy+sinycosx-cosxsiny=sinxcosy cosxcosy+sinxsiny-sinxsiny=cosxcosy sinacosb-sinacosb+sinbcosa=sinbcosa cosacosb-cosacosb-sinasinb=-sinasinb