cos(x+y)=1/5,cos(x-y)=3/5则tanx.tany=?
帮我解
人气:380 ℃ 时间:2020-03-25 03:40:38
解答
cos(x+y)+cos(x-y)=2cos[(x+y+x-y)/2]cos[(x+y-x+y)/2]=2cosx*cosy=4/5
cos(x+y)-cos(x-y)=-2sin[(x+y+x-y)/2]sin[(x+y-x+y)/2]=-2sinx*siny=-2/5
cosx*cosy=2/5
sinx*siny=1/5
tanx.tany=(sinx*siny)/(cosx*cosy)=1/2
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