\begin{array}{c}x=\cos x的解是\\\displaystyle x=\frac{\pi}{2} \exp\left ( \frac{1}{\pi}\int_{0}^{1}\frac{1}{t}\arctan\frac{\left ( \pi t^2+2t \right )\ln\frac{1+\sqrt{1-t^2} }{t} }{t^2\ln^2\frac{1+\sqrt{1-t^2} }{t}-\pi t-1 } \mathrm{d}t \right ) \\≈0.7390851332151606\\\exp(x)=e^x\\\ln^nx=(\ln x)^n\end{array}