f(x) is a real valued function defined for x≥0 such that f(0)=0, f(x+1)=f(x)+x for all x, and
f(x) < \frac{1}{2}f\left(x - \frac{1}{2}\right)+\frac{1}{2}f\left(x + \frac{1}{2}\right) \text{for all} x \geq \frac{1}{2}
Show that f(21) is uniquely determined. functionalFunctional inequalityalgebra