Use calculus to find the open intervals on which the function f(x) = x82 - x-12 is increasing or decreasing:
a. (-infty, 0) increasing, (0, infty) decreasing
b. (0, infty) increasing, (-infty, 0) decreasing
c. (-infty, 0) decreasing, (0, infty) increasing
d. (0, infty) decreasing, (-infty, 0) increasing