Steiner's problem

Steiner's problem

Steiner's problem is the problem of finding the maximum of the function

: f(x)=x^{1/x}.,

It is named after Jakob Steiner.

The maximum is at x=e, where "e" denotes the base of natural logarithms. One can determine that by solving the equivalent problem of maximizing

: g(x)=ln f(x) = frac{ln x}{x}.

The derivative of g can be calculated to be

: g'(x)= frac{1-ln x}{x^2}.

It follows that g'(x) is positive for 0 and negative for x>e, which implies that g(x) (and therefore f(x)) increases for 0 and decreases for x>e. In conclusion, x=e is the unique global maximum of f(x).


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