sin6π1r=1∑13sin(4π+(r−1)6π)sin(4π+6rπ)sin[(4π+6rπ)−(4π)−(r−1)6π] $\begin{aligned}
& \frac{1}{\sin \frac{\pi}{6}} \sum_{\mathrm{r}=1}^{13}\left(\cot \left(\frac{\pi}{4}+(\mathrm{r}-1) \frac{\pi}{6}\right)-\cot \left(\frac{\pi}{4}+\frac{\mathrm{r} \pi}{6}\right)\right) \
& =2 \sqrt{3}-2=\alpha \sqrt{3}+\mathrm{b}
\end{aligned}Soa^2+b^2=8$