Given the following cost function, where t is the quantity of some product.
$$C(t) = 1/3t^3 - 7t^2 +11t + 50$$
here is a graph between $t= 0$ and $t = 25$
We are asked if this function is convex or concave?
Technically it is neither, but I am asking, in the context of economics, do we have to define intervals and say, between $0$ and $4.11$, it is concave, and for $t>4.12$ we have a convex function?