已知3cos（2x+y）+5cosy=0,则tan(x+y)tanx的值是线上等!_数学解答

已知3cos（2x+y）+5cosy=0,则tan(x+y)tanx的值是
线上等!

人气：213 ℃　时间：2020-01-30 10:52:46

解答

cos(2x+y)=cos[(x+y)+x]=cos(x+y)cosx-sin(x+y)sinxcosy=cos[(x+y)-x]=cos(x+y)cosx+sin(x+y)sinx3cos（2x+y）+5cosy=8cos(x+y)cosx+2sin(x+y)sinx=0tan(x+y)tanx=-4