for a rational, we find the vertical asymptotes where its denominator is 0, thus
(x-2)(x+1) = 0, gives us two vertical asymptotes when that happens, x = 2 and x = -1.
if we expand the denominator, we'll end up with a quadratic equation, namely a 2nd degree equation, whilst the numerator is of 3rd degree. Whenever the numerator has a higher degree than the denominator, the rational has no horizontal asymptotes, however when the numerator is exactly 1 degree higher like in this case, it has an oblique asymptote instead.
