已知3cos（2x+y）+5cosy=0,则tan(x+y)tanx的值是
线上等!
人气：152 ℃ 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
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