x＋x分之一 ＝4,
两边平方得x^2+2+1/x^2=16
x^2+1/x^2=14
（x四次方＋x平方＋1）分之x平方
=1/[(x^4+x^2+1)/x^2]
=1/[x^2+1+1/x^2]
=1/[14+1]
=1/15