我不帅但不坏
幼苗
共回答了4个问题 举报
令arctanX1=a,arctanX2=b,
则原式等价于arctanX1+arctanX2=a+b,
因为X1+X2=sin(π/5)=sin(4π/5)=tan(a)+tan(b)
X1X2=cos(4π/5)=tan(a)tan(b)
tan(a+b)=tan(a)+tan(b)/[1-tan(a)tan(b)]=sin(4π/5)/[1-cos(4π/5)]
所以arctanX1+arctanX2=arc{sin(4π/5)/[1-cos(4π/5)]}+180度乘以k,
1年前
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