已知x+1/x=8/7,则x方/x四次方+x方+1=?

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答：
x+1/x=8/7
(x^2)/(x^4+x^2+1)
=1/(x^2+1+1/x^2)
=1/[(x+1/x)^2-1]
=1/[(8/7)^2-1]
=1/(64/49-1)
=49/25

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