Find A,B and C.

Question

Consider the function f(x)=5x+6x^-1. For this function there are four important intervals (-infinity, A], [A,B), (B,C), and [C, infinity) where A and C are the critical numbers and the function is not defined at B.

Find A

Find B

Find C 

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

(-infinity, A]: 

[A, B):

(B,C]:

[C, infinity):

Answer 1

There is an error in the problem formulation. Probably, first term should contain x-square. Otherwise, this is a straight line y=11x-1 and A,B,C,D do not have any sense.

Answer 2

I answered this already. Check back for my answer!