3. 試求 _x→∞ x^2 e^-x = ? (A) e (B) 1 (C) 0 (D) ∞

12. 試求 \(\int \frac{1}{x^2(a-bx)} dx = ?\) (A) \(\frac{b}{a^2}\log_e \left|\frac{x}{a-bx}\right| - \frac{1}{ax} + C\) (B) \(\frac{b}{a^2}\log_e \left|\frac{x}{a-bx}\right| - \frac{1}{bx} + C\) (C) \(\frac{b^2}{a}\log_e \left|\frac{x}{a-bx}\right| - \frac{1}{ax} + C\) (D) \(\frac{b^2}{a^2}\log_e \left|\frac{x}{a-bx}\right| - \frac{1}{ax} + C\)