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

a) $$y-20+\frac{5y-2}{4y}+y^2 = \frac{4y(y-20)}{4y} + \frac{5y-2}{4y} + \frac{4y^3}{4y} = \frac{4y^2-80y+5y-2+4y^3}{4y} = \frac{4y^3+4y^2-75y-2}{4y}$$ 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) $$\frac{a+5}{7}-\frac{7a-3}{a^2+5a} = \frac{a+5}{7}-\frac{7a-3}{a(a+5)} = \frac{a(a+5)^2 - 7(7a-3)}{7a(a+5)} = \frac{a(a^2+10a+25) - 49a+21}{7a(a+5)} = \frac{a^3+10a^2+25a - 49a+21}{7a(a+5)} = \frac{a^3+10a^2-24a+21}{7a(a+5)}$$