(sina+cosa)×(sinB-cosB)=sin(B-a)- cos (B+a)

Question

(sina+cosa)×(sinB-cosB)=sin(B-a)- cos (B+a)

Answer 1

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