x^-1 + x^-2 + x^-3 = 1/x + 1/x^2 + 1/x^3 = (x^2 + x + 1)/x^3
(x + x^2 + x^3) : (x^2 + x + 1) / x^3 = x(1 + x + x^2) * x^3 /(1 + x + x^2) = x*x^3 = x^4
x^-1 + x^-2 + x^-3 = 1/x + 1/x^2 + 1/x^3 = (x^2 + x + 1)/x^3
(x + x^2 + x^3) : (x^2 + x + 1) / x^3 = x(1 + x + x^2) * x^3 /(1 + x + x^2) = x*x^3 = x^4