三角函数的,积化和差,和差化积,的公式,有什么口诀好记下来,老师教过一次,不过说的比较方言,不理解,所以记不下来,

Question

三角函数的,积化和差,和差化积,的公式,有什么口诀好记下来,老师教过一次,不过说的比较方言,不理解,所以记不下来,

Answer 1

和差化积
sinx+siny=2sin[(x+y)/2]cos[(x-y)/2]
sinx-siny=2cos[(x+y)/2]sin[(x-y)/2]
cosx+cosy=2cos[(x+y)/2]cos[(x-y)/2]
cosx-cosy=-2sin[(x+y)/2]sin[(x-y)/2]
积化和差
sinxsiny=-1/2[cos(x+y)-cos(x-y)]
cosxcosy=1/2[cos(x+y)+cos(x-y)]
sinxcosy=1/2[sin(x+y)+sin(x-y)]
cosxsiny=1/2[sin(x+y)-sin(x-y)]