13nπ+(−1)nπ6\frac{1}{3} \mathrm{n} \pi+(-1)^{\mathrm{n}} \frac{\pi}{6}31nπ+(−1)n6π
13nπ+π6\frac{1}{3} n \pi+\frac{\pi}{6}31nπ+6π
13nπ−π18\frac{1}{3} n \pi-\frac{\pi}{18}31nπ−18π
13nπ+(−1)nπ18\frac{1}{3} \mathrm{n} \pi+(-1)^{\mathrm{n}} \frac{\pi}{18}31nπ+(−1)n18π