(x^3-2x^2+ax+2)/(x^2-4x+1)=x+2
x^3-2x^2+ax+2=(x+2)(x^2-4x+1)
x^3-2x^2+ax+2=x^3-4x^2+x+2x^2-8x+2
x^3-2x^2+ax+2=x^3-2x^2-7x+2
a=-7