Question

f(x) = -x^4-7x^3+5x-4

Find where concaave up and concave down.

I've found the inflection points of 0, 7/2. How do I know the intervals where concave up and concave down?

Answer 1

Have you taken the second derivative and found the critical points, yet?

Answer 2

Well, you clearly did because you already found the inflection points :)

Answer 3

So, when you already found the critical points
if you have f"<0 then that is concave down
if you have f">0 then it is concave up.