\[\boxed{\mathbf{849\ (849).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ \frac{8}{x} - \frac{5}{y} = \frac{8y - 5x}{\text{xy}}\]
\[2)\ \frac{7}{\text{ab}} + \frac{5}{b} = \frac{7 + 5a}{\text{ab}}\]
\[3)\ \frac{5}{24xy} - \frac{7}{18xy} = \frac{15 - 28}{72xy} =\]
\[= \frac{- 13}{72xy}\]
\[4)\ \frac{5b^{2} - 8b + 1}{a^{2}b^{2}} - \frac{2b - 1}{a^{2}b} =\]
\[= \frac{5b^{2} - 8b + 1 - 2b^{2} + b}{a^{2}b^{2}} =\]
\[= \frac{3b² - 7b + 1}{a²b²}\]