I am facing a maximisation problem, and I need to check the concavity of my objective function. (Actually, quasi-concavity would be sufficient, but I have no idea how to check it).
In poor words, I have to maximise f(x) wrt x. This is what I have so far:

```
function = (k*f)*f + 3 f + (1 - f) k (1 + f) t
first = D[function, f]
second = Simplify[ D[first, f]]

```

Thus, the second order condition is `-2 k (-1 + t)`, where k and t are parameters which can vary in the range [0,1]. I want to determine under which conditions on the parameters the objective function is concave (or quasi-concave). How can I do it?