As with all limits where x→∞ or x→−∞,compare the highest-power term in the numerator with the highest-power term in the denominator. Be sure to consider coefficients.
This is Ana's method to find a derivative. If you need more guidance, refer to the hints in problem 3-110 part (b).
Or you could multiply the numerator and the denominator by the conjugate of
When you evaluate at x = 6, there is a 0 in the denominator. Perhaps you can cancel it out. Try factoring.
Refer to the hint in part (a).