若X+1/X=3则X^2/X^4+X^2+1=____
问题描述:
若X+1/X=3则X^2/X^4+X^2+1=____
答
8
X^2/X^4+X^2+1=1/X^2+X^2+1=(X+1/X)^2-1=8
答
x+1/x=3,两边平方,
x^2+1/x^2+2=9
x^2+1/x^2=7
(x^4+x^2+1)/x^2=x^2+1+1/x^2=7+1=8
x^2/(x^4+x^2+1) = 1 / [(x^4+x^2+1)/x^2] = 1/8