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问题: x/x^2+x+1=a 求x^2/x^4+x^2+1的值

解答:

x/(x^2+x+1)=a ==> (x^2+x+1)/x =1/a ==> x +1/x =(1-a)/a
x^2/x^4+x^2+1 =1/[(x +1/x)^2 -1]
= 1/[(1-a)^2/a^2 -1]
= a^2/(1-2a)