x²-4x+1=0 两边同时除以x得
x-4+1/x=0
x+1/x=4
(1)x²+1/x²
=(x²+2+1/x²)-2
=(x+1/x)²-2
=4²-2
=16-2
=14
(2)x²/(x的4次方+x²+1) 分子分母同时除以x²得
=1/(x²+1+1/x²)
=1/[(x²+1/x²)+1]
=1/(14+1)
=1/15