x^3 - 13x^2 + 40x - 40 =0
x^3 - 4x^2+4x-9x^2 + 36x - 36-4=0
x(x-2)^2-9(x-2)^2-4=0
(x-9)(x/2-1)^2=1
x/2-1=y
(2y+7)y^2=1,-1