v=5y^3+31y^2+6y

V = y(5y^2+31y+6).

A*C = 5*6 = 30 = 1*30.
V = y(5y^2+(y+30y)+6) = 0.
y(5y^2+y)(30y+6) = 0.
y*y(5y+1)6(5y+1) = 0
6y^2(5y+1)(5y+1) = 0.

6y^2 = 0, Y = 0.

5y+1 = 0, Y = -1/5.