Y的平方+3Y-1=0
y+3-1/y=0
y-1/y=-3
(y-1/y)^2=9
y^2+1/y^2-2=9
y^2+1/y^2=11
(y^2+1/y^2)=121
y^4+1/y^4+2=121
y^4+1/y^4=119
(Y的四次方)÷(Y的八次方-3Y的四次方+1)
=1/(y^4-3+1/y^4)
=1/(119-3)
=1/116