26. Find the minimum value of the expression $\left(a^{2}+x^{2}\right) / x$, where $a>0$ is a constant, and $x>0$ is a variable.
61.26. Answer. $2 a$. Hint. $\left(a^{2}+x^{2}\right) / x=a(a / x+x / a) \geqslant 2 a$.