(2 points) Let f(x)=2+48xx^3. Find (a) the intervals on which f is increasing, (b) the intervals on which f is decreasing, (c) the open intervals on which f is concave up, (d) the open intervals on which f is concave down, and (e) the x-coordinates of all inflection points.

(a) f is increasing on the interval(s) (b) f is decreasing on the interval(s) (c) f is concave up on the open interval(s) (d) f is concave down on the open interval(s) (e) the x coordinate(s) of the points of inflection are

Notes: In the first four boxes, your answer should either be a single interval, such as [0,1), a comma separated list of intervals, such as (-inf, 2), (3,4], or the word "none".

In the last box, your answer should be a comma separated list of x values or the word "none".

I have worked out this problem for a while now and I know the answers to c, d, and e:

(c) (-inf,0)

(d) (0,inf)

(e) 0

For (a) and (b), I got (-4,4) and (-inf,-4),(4,inf) respectively, but the system doesn't accept those at all, even after checking the answer after submitting my own work. What do I change as answers for (a) and (b) so the system accepts those? I would appreciate the help.