Question

貌似不难,sin（a+b）cos（c-b）-cos（b+a）sin（b-c）sin（a-b）sin（b-c）-cos（a

Answer 1

1.sin(a+b)cos(c-b)-cos(b+a)sin(b-c)=sin(a+b)cos(c-b)+cos(a+b)sin(c-b)

=sin[(a+b)+(c-b)]=sin(a+c)

2.sin(a-b)sin(b-c)-cos(a-b)cos(c-b)=sin(a-b)sin(b-c)-cos(a-b)cos(b-c)

=-[cos(a-b)cos(b-c)-sin(a-b)sin(b-c)]=-cos[(a-b)+(b-c)]=-cos(a-c)

=cos(a-c)

参考正弦和余弦和与差的公式即可