Question

(Sin a + cos a )×( sin b -cos b)=sin( b- a)-cos(b+a)

Answer 1

sinasinb-sinacosb+cosasinb-cosacosb=sin(a-b)-cos(a+b)
sinacosb-cosasinb=sin(a-b)
cos(a+b)=cosacosb-sinasinb