6. Let the quadratic function $f(x)=a x^{2}+b x+c(a>0)$ satisfy $f(5-x)=f(5+x)$. Then the order from smallest to largest of $f(\sqrt{40})$, $f(2 \pi)$, and $f\left(5 \sin 45^{\circ}\right)$ is $\qquad$.
$\begin{array}{l}\text { 6. } f(2 \pi)<f(\sqrt{40})<f\left(5 \sin 45^{\circ}\right) . \\ |\sqrt{40}-5| \approx 1.32,|2 \pi-5| \approx 1.28, \\ \left|\frac{5}{\sqrt{2}}-5\right| \approx 1.46 .\end{array}$