f(x) it self has roots aprox. -1.75 and 1.75. And 0. It's respectively is neg, pos, neg, pos. That is obvious from the graph.
f´(x) has roots at -1 and 1. And is pos, neg, pos.
How can I view the double derivative f´´(x)? I know if the graph "smiles" f´´(x) is positive and if it is sad f´´(x) < 0.