Решение:

1. a) $$\frac{3x-1}{x^2} - \frac{x-9}{3x} = \frac{3(3x-1) - x(x-9)}{3x^2} = \frac{9x - 3 - x^2 + 9x}{3x^2} = \frac{-x^2 + 18x - 3}{3x^2}$$
2. б) $$\frac{1}{2a-b} - \frac{1}{2a+b} = \frac{(2a+b)-(2a-b)}{(2a-b)(2a+b)} = \frac{2a+b-2a+b}{4a^2-b^2} = \frac{2b}{4a^2-b^2}$$
3. в) $$\frac{5}{c+3} - \frac{5c-2}{c^2+3c} = \frac{5}{c+3} - \frac{5c-2}{c(c+3)} = \frac{5c - (5c-2)}{c(c+3)} = \frac{5c - 5c + 2}{c(c+3)} = \frac{2}{c(c+3)}$$