\[\boxed{\text{40\ (40).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ x - 5y = \frac{2 \cdot (x - 5y)}{2} =\]
\[= \frac{2x - 10y}{2}\]
\[2)\ x - 5y = \frac{x(x - 5y)}{x} =\]
\[= \frac{x^{2} - 5xy}{x}\]
\[3)\ x - 5y = \frac{4y^{3}(x - 5y)}{4y^{3}} =\]
\[= \frac{4xy^{3} - 20y^{4}}{4y^{3}}\]
\[4)\ x - 5y = \frac{(x - 5y)^{2}(x + 5y)}{x^{2} - 25y^{2}}\]