б) √n / √n-13 + 13/13-√n

б) $$\frac{\sqrt{n}}{\sqrt{n} - 13} + \frac{13}{13 - \sqrt{n}} = \frac{\sqrt{n}}{\sqrt{n} - 13} - \frac{13}{\sqrt{n} - 13} = \frac{\sqrt{n} - 13}{\sqrt{n} - 13} = 1$$.

Ответ: 1