2. Представьте в виде дроби: a) $$y - \frac{20}{4y} + \frac{5y-2}{y^2}$$ b) $$\frac{1}{5c-d} - \frac{1}{5c+d}$$ c) $$\frac{a+5}{7} - \frac{7a-3}{a^2+5a}$$

a) $$y - \frac{20}{4y} + \frac{5y-2}{y^2} = y - \frac{5}{y} + \frac{5y-2}{y^2} = \frac{y^3}{y^2} - \frac{5y}{y^2} + \frac{5y-2}{y^2} = \frac{y^3 - 5y + 5y - 2}{y^2} = \frac{y^3 - 2}{y^2}$$ б) $$\frac{1}{5c-d} - \frac{1}{5c+d} = \frac{(5c+d) - (5c-d)}{(5c-d)(5c+d)} = \frac{5c+d - 5c+d}{(5c)^2 - d^2} = \frac{2d}{25c^2 - d^2}$$ в) $$\frac{a+5}{7} - \frac{7a-3}{a^2+5a} = \frac{a+5}{7} - \frac{7a-3}{a(a+5)} = \frac{a(a+5)^2 - 7(7a-3)}{7a(a+5)} = \frac{a(a^2 + 10a + 25) - 49a + 21}{7a(a+5)} = \frac{a^3 + 10a^2 + 25a - 49a + 21}{7a(a+5)} = \frac{a^3 + 10a^2 - 24a + 21}{7a(a+5)}$$