3. |cosx|=2+4Σ(-1)n+1cos 2nx ππη-1 4n² Y tg(2n+x) n→∞∫∫ xn+1dx

Ответ:

1. $$|cos x| = \frac{2}{\pi} + \frac{4}{\pi} \sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{4n^2} cos 2nx - \frac{Y}{\lim_{n \to \infty}} \int \int x^{n+1} dx \cdot tg(2n+x)$$