Tính giới hạn a. \(\lim_{x \to -2} \frac{(3x+1)(2-3x)}{x+1}\) b. \(\lim_{x \to 0} \frac{1+x+x^{2}+x^{3}}{1+x}\) c. \(\lim_{x \to 1} \frac{\sqrt{3x^{2}+1-x}}{x-1}\) d. \(\lim_{x \to 2} \frac{5x-1}{2x+7}\) e. \(\lim_{x \to 2} \frac{\sqrt{x^{2}-x+1}}{x-1}\) f. \(\lim_{x \to -1} \frac{\sqrt{x+8}-3}{x-2} = 0\)
