sinx-siny=-2/3,cosx-cosy=2/3 求cos(x-y)

问题描述:

sinx-siny=-2/3,cosx-cosy=2/3 求cos(x-y)

sinx-siny=-2/3 cosx-cosy=2/3(sinx-siny)²+(cosx-cosy)²=(-2/3)²+(2/3)²sin²x-2sinxsiny+sin²y+cos²x-2cosxcosy+cos²y=8/92-2(cosxcosy+sinxsiny)=8/92cos(x-y)=10/9cos(x...