Question

关于三角函数的我不知道怎么由第二步到第三步

Answer 1

是不是这个

(sin^A+sin^B)sin(A-B)=(sin^A-sin^B)sin(A+B)

sin^A*(sin(A+B)-sin(A-B))=sin^B*(sin(A-B)+sin(A+B))

乘出来

sin^A*sin(A-B)+sin^B*sin(A-B)=sin^A*sin(A+B)-sin^B*sin(A+B)

移项

sin^A*sin(A+B)-sin^A*sin(A-B)=sin^B*sin(A-B)+sin^B*sin(A+B)

所以sin^A*(sin(A+B)-sin(A-B))=sin^B*(sin(A-B)+sin(A+B))