一个强不等式

1+1=？

比较复杂的不等式
\begin{aligned}
& \forall x \in\left[-\frac{\pi}{2}, \frac{\pi}{2}\right], k \leq \frac{\pi^2}{6}-1 \\
& \left(\sqrt{\left|1-\frac{4}{\pi^2} x^2\right|}\right)^{\frac{k \pi^2}{4}} e^{\frac{(k-1) \pi^2}{4}\left(1-\sqrt{1-\frac{4}{\pi^2} x^2}\right)} \geq \cos (x)
\end{aligned}