\[\begin{array}{l}
\frac{7}{{5{\rm{x}}}}\\
\frac{4}{{x - 2y}}\\
\frac{{x - y}}{{8{y^2} - 2{{\rm{x}}^2}}} = \frac{{x - y}}{{2\left( {4{y^2} - {x^2}} \right)}} = \frac{{x - y}}{{2\left( {2y - x} \right)\left( {2y + x} \right)}} = \frac{{y - x}}{{2\left( {x - 2y} \right)\left( {x + 2y} \right)}}\\
dk:x \ne 0;x \ne 2y;x \ne - 2y\\
M{\rm{S}}C = 10{\rm{x}}(x - 2y)(x + 2y)\\
\frac{7}{{5{\rm{x}}}} = \frac{{7.2\left( {x - 2y} \right)\left( {x + 2y} \right)}}{{10{\rm{x}}(x - 2y)(x + 2y)}} = \frac{{14\left( {{x^2} - 4{y^2}} \right)}}{{10{\rm{x}}(x - 2y)(x + 2y)}} = \frac{{14{{\rm{x}}^2} - 56{y^2}}}{{10{\rm{x}}(x - 2y)(x + 2y)}}\\
\frac{4}{{x - 2y}} = \frac{{4.10{\rm{x}}\left( {x + 2y} \right)}}{{10{\rm{x}}(x - 2y)(x + 2y)}} = \frac{{40{\rm{x}}\left( {x + 2y} \right)}}{{10{\rm{x}}(x - 2y)(x + 2y)}} = \frac{{40{{\rm{x}}^2} + 80{\rm{x}}y}}{{10{\rm{x}}(x - 2y)(x + 2y)}}\\
\frac{{x - y}}{{8{y^2} - 2{{\rm{x}}^2}}} = \frac{{5{\rm{x}}\left( {y - x} \right)}}{{10{\rm{x}}(x - 2y)(x + 2y)}} = \frac{{5{\rm{x}}y - 5{{\rm{x}}^2}}}{{10{\rm{x}}(x - 2y)(x + 2y)}}
\end{array}\]