Представьте в виде дроби: a) $$\frac{3x-1}{3x} + \frac{x-9}{3x}$$; б) $$\frac{1}{2a-b} - \frac{1}{2a+b}$$; в) $$\frac{5}{c+3} - \frac{5c-2}{c^2+3c}$$

a) $$\frac{3x-1}{3x} + \frac{x-9}{3x} = \frac{3x - 1 + x - 9}{3x} = \frac{4x - 10}{3x} = \frac{2(2x - 5)}{3x}$$
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) $$\frac{5}{c+3} - \frac{5c-2}{c^2+3c} = \frac{5}{c+3} - \frac{5c-2}{c(c+3)} = \frac{5c-(5c-2)}{c(c+3)} = \frac{5c-5c+2}{c(c+3)} = \frac{2}{c(c+3)}$$