x²-4x+1=0
等式两边同除以x
x- 4 +1/x=0
x +1/x=4
x²/(x⁴+x²+1)
=1/(x²+1 +1/x²)/这一步是上一步分子分母同除以x²得到
=1/[(x+1/x)²-1]
=1/(4²-1)
=1/15