Concavity

[stadtaffe2]

For which values of X is y=x^4-8x^2 concave up?

The answer it gives me is a fraction that i do not understand and do not know how to write on this website. If you can help explain it, it will be greatly appreciated.

 

[galactus]

First, find the second derivative

 

[pka]

There is nothing like a graph.