lim (x^2-5) / (x^3+x+1) = (3^2 - 5) / (3^3+3+1) = 4 / 31
lim (x^2-4x+3) / (x-1) = lim (x-1)(x-3) / (x-1) = lim (x-3) = 1 - 3 = -2
lim (x^2 + 2x + 3) / (2x^2 + 3x + 4) = lim (1 + 2/x + 3/x^2) / (2 + 3/x + 4/x^2) = (1+0+0) / (2+0+0) = 1/2
