Given number: $$\sin{\left(\frac{\pi}{n} \right)}$$ It is a series of species $$a_{n} \left(c x - x_{0}\right)^{d n}$$ - power series. The radius of convergence of a power series can be calculated by the formula: $$R^{d} = \frac{x_{0} + \lim_{n \to \infty} \left|{\frac{a_{n}}{a_{n + 1}}}\right|}{c}$$ In this case $$a_{n} = \sin{\left(\frac{\pi}{n} \right)}$$ and $$x_{0} = 0$$ , $$d = 0$$ , $$c = 1$$ then $$1 = \lim_{n \to \infty} \left|{\frac{\sin{\left(\frac{\pi}{n} \right)}}{\sin{\left(\frac{\pi}{n + 1} \right)}}}\right|$$ Let's take the limit we find