f(x) = 2x^2 + x - 3
g(x) = x - 1
f(x).g(x) - [f(x) + g(x)] = (2x^2 + x - 3) (x - 1) - [2x^2 + x - 3 + x - 1]
f(x).g(x) - [f(x) + g(x)] = (2x^3 - 2x^2 + x^2 - x - 3x + 9) - [2x^2 + 2x - 4]
f(x).g(x) - [f(x) + g(x)] = (2x^3 - x^2 - 4x + 9) - [2x^2 + 2x - 4]
f(x).g(x) - [f(x) + g(x)] = 2x^3 - x^2 - 4x + 9 - 2x^2 - 2x + 4
f(x).g(x) - [f(x) + g(x)] = 2x^3 - 3x^2 - 6x + 13
