已知x=2n/1+n2,y=1-n2/1+n2,求x2+y2的值
问题描述：
已知x=2n/1+n2,y=1-n2/1+n2,求x2+y2的值
答
x=2n/1+n2,y=1-n2/1+n2
x2+y2
=[(4n^2+(1-n^2)^2]/(1+n^2)^2
=(1+n^2)^2/(1+n^2)^2
=1
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