Question

1)sin(x+y)-cosxsiny
2)cos(x-y)-sinxsiny
3)sina cosB_sin(a-B)

Answer 1

1)sin(x+y)-cosxsiny=sinxcosy+sinycosx-cosxsiny=sinxcosy
2)cos(x-y)-sinxsiny=cosxcosy+sinxsiny-sinxsiny=cosxcosy
3)sinacosb-sin(a-b)=sinacosb-(sinacosb-sinbcosa)=sinacosb-sinacosb+sinbcosa=sinbcosa