已知tan(x+y)=3,tan(x-y)=5则tan2x等于

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已知tan(x+y)=3,tan(x-y)=5则tan2x等于已知tan(x+y)=3,tan(x-y)=5则tan2x等于已知tan(x+y)=3,tan(x-y)=5则tan2x等于tan(x+y

已知tan(x+y)=3,tan(x-y)=5则tan2x等于
已知tan(x+y)=3,tan(x-y)=5则tan2x等于

已知tan(x+y)=3,tan(x-y)=5则tan2x等于
tan(x+y)=3,tan(x-y)=5
tan(2x) = tan{(x+y)+(x-y)}
= {tan(x+y) + tan(x-y) } / {1-tan(x+y)tan(x-y)}
= (3+5)/(1-3*5)
=8/(-14)
=-4/7

-4/7

tan (2x)= tan[(x+y) +(x-y)]
=[tan(x+y) + tan(x-y)]/[1-tan(x+y)*tan(x-y)]
=[3+5]/[ 1- 3*5]
= - 4/7

tan2x=tan(x+y+x-y)=(tan(x+y)+tan(x-y))/(1-tan(x+y)tan(x-Y)=8/(-14)=-(4/7)