(4y2+5y+1)/(y4-1)
Let's first factor the numerator and the denominator
[(4y+1)(y+1)]/(y+1)(y-1)(y2+1)]
Notice there's a y+1 factor in both the numerator and denominator. They cancel one another so we are left with
(4y+1)/[(y+1)(y2+1)]
which equals
(4y+1)/(y3+y2+y+1)