Задание 1, 2, 7
1. [m]\frac{sin\frac{2\pi}{2n+1}}{\sqrt{n}}[/m] 2. [m]sin\frac{(2n+1)}{(n-1)^2\cdot (n)^2}[/m] 7. [m](-1)^{n}arctg\frac{1}{n}[/m]