Unexpected result from FindMaximum?

Hello,
I’m new to Mathematica and I want to find the positive maximum value of a function, but so far I always ended up with either a negative value or the value doesn’t even show up.

Maximization.nb (4.54 KB)

Try:

FindMaximum[f[x], {x, 1/3}] (* With starting point 1/3*)
NMaximize[{f[x], 0 < x < 1}, x]

(*{1.09904*10^6, {x -> 0.263896}}*)

Maximization-ver2.nb (23.2 KB)