Выполните действие: a) $$rac{b - 3}{2b} + rac{b + 12}{8b}$$; б) $$rac{1}{n - 5} - rac{1}{n + 5}$$

a) $$rac{b - 3}{2b} + rac{b + 12}{8b} = rac{4(b - 3) + (b + 12)}{8b} = rac{4b - 12 + b + 12}{8b} = rac{5b}{8b} = rac{5}{8}$$

б) $$rac{1}{n - 5} - rac{1}{n + 5} = rac{(n + 5) - (n - 5)}{(n - 5)(n + 5)} = rac{n + 5 - n + 5}{n^2 - 25} = rac{10}{n^2 - 25}$$