28. Given the following 3 propositions: (1) If $a, b \in \mathrm{R}$, then $\frac{a+b}{2}$ $\geqslant \sqrt{a b}$; (2) $x \in \mathrm{R}$, then $x^{2}+1>x$; (3) If $x \in \mathrm{R}$ and $x \neq 0$, then $x+\frac{1}{x} \geqslant 2$, the true propositions are $\qquad$.