Question

怎样用两角和的正弦公式推导两角差的正弦公式?

Answer 1

两角和正弦公式为：
sin(a+b)=sin(a)*cos(b)+sin(b)*cos(a);
所以：
sin(a-b)=sin[a+(-b)]
=sin(a)*cos(-b)+sin(-b)*cos(a)
=sin(a)*cos(b)-sin(b)*cos(a);