Thanks for the reply.
Sorry but i don't understand how these are counterexample. Beside that they aren't derivable in 0, if i multiply them with 2x i obtain functions that the max is in a or b and the new function is only increasing or decreasing
Probably i failed to write that 0=<a<b<+inf
Homework Statement
I have y=2x*f(x).
f is strictly monotonically decreasing, non-negative, derivable and continuous in the close interval [0,c] with c>=1. it doesn't change its concavity in the interval, maybe beside at x=c/2. Note that 2x has the same properties but is monotonically...