Consider the function f(x) = 7x + 8x ^-1. For this function there are four important intervals: (-\infty, A], [A,B),(B,C), and [C,\infty) where A, and C are the critical numbers and the function is not defined at B.

Find A

and B

and C

For each of the following intervals, tell whether f(x) is increasing or decreasing.

(i infty, A]:

[A,B):

(B,C]:

[C,infty):

Any help will be appreciated!