\[\boxed{\mathbf{623\ (623)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ не\ нарушится:\]
\[x\ :y = a\ :b\]
\[\frac{8x}{8y} = \frac{a}{b}\]
\[\frac{x}{y} = \frac{a}{b}.\]
\[2)\ не\ нарушится:\]
\[x\ :y = a\ :b\]
\[\frac{x}{2}\ :\frac{y}{2} = \frac{5a}{5b}\]
\[\frac{x}{2} \cdot \frac{y}{2} = \frac{a}{b}\]
\[\frac{x}{y} = \frac{a}{b}.\]
\[3)\ нарушится:\]
\[x\ :y = a\ :b\]
\[x\ :\frac{y}{3,6} = \frac{a}{3,6}\ :b\]
\[x \cdot \frac{3,6}{y} = \frac{a}{3,6} \cdot \frac{1}{b}\]
\[\frac{3,6x}{y} = \frac{a}{3,6b}.\]