Verified answer

x^4+2x^3-16x^2-2x+15 = x^4 + x^3 + x^3 + x^2 - 17x^2 - 17x + 15x + 15 =

= x^3(x+1) + x^2(x+1) - 17x(x+1) + 15(x+1) =

=(x+1)(x^3 + x^2 - 17x + 15)

(x+1)(x^3+ax^2-17x+b)

a=1

b=15