Представление в виде дроби

a) $$\frac{3x - 1}{x^2} - \frac{x - 9}{3x} = \frac{3(3x - 1) - x(x - 9)}{3x^2} = \frac{9x - 3 - x^2 + 9x}{3x^2} = \frac{-x^2 + 18x - 3}{3x^2}$$

б) $$\frac{1}{2a - b} - \frac{1}{2a + b} = \frac{(2a + b) - (2a - b)}{(2a - b)(2a + b)} = \frac{2a + b - 2a + b}{4a^2 - b^2} = \frac{2b}{4a^2 - b^2}$$

в) $$\frac{5}{c + 3} - \frac{5c - 2}{c^2 + 3c} = \frac{5}{c + 3} - \frac{5c - 2}{c(c + 3)} = \frac{5c - (5c - 2)}{c(c + 3)} = \frac{5c - 5c + 2}{c(c + 3)} = \frac{2}{c(c + 3)} = \frac{2}{c^2 + 3c}$$