(x-1)(x^3-16x^2-x+16)=0
x=1
x^3-16x^2-x+16
(x^3-16x^2)-(x-16)
(x-16)(x^2-1)=0
x-16=0
x=16
x^2-1=0
x=-1
X=-1, X=1, X=16
(x-1)(x^3-16x^2-x+16)=0
x=1
x^3-16x^2-x+16
(x^3-16x^2)-(x-16)
(x-16)(x^2-1)=0
x-16=0
x=16
x^2-1=0
x=1
x=-1
X=-1, X=1, X=16