7. Given the function $f(x)=\sqrt{x^{2}+1}-\frac{2}{5} a x$, where $a>0$, is a monotonic function on the interval $[0,+\infty)$, then the range of values for $a$ is $\qquad$ .
$f^{\prime}(x)=\frac{x}{\sqrt{x^{2}+1}}-\frac{2}{5} a$, since $\frac{x}{\sqrt{x^{2}+1}} \in[0,1)$,
thus when $f(x)$ is monotonically increasing, $\frac{2}{5} a \leqslant 0 \Rightarrow a \leqslant 0$, which is discarded; when $f(x)$ is monotonically decreasing, $\frac{2}{5} a \geqslant 1 \Rightarrow a \geqslant \frac{5}{2}$. Therefore, the range of $a$ is $\left[\frac{5}{2},+\infty\right)$.