Đáp án:
$\begin{array}{l}
7)a)\frac{{x - 5}}{5} + \frac{{1 - x}}{5} = \frac{{x - 5 + 1 - x}}{5} = \frac{{ - 4}}{5}\\
g)\frac{{2{x^2} - xy}}{{x - y}} + \frac{{xy + {y^2}}}{{y - x}} + \frac{{2{y^2} - {x^2}}}{{x - y}}\\
= \frac{{2{x^2} - xy - \left( {xy + {y^2}} \right) + 2{y^2} - {x^2}}}{{x - y}}\\
= \frac{{2{x^2} - xy - xy - {y^2} + 2{y^2} - {x^2}}}{{x - y}}\\
= \frac{{{x^2} - 2xy + {y^2}}}{{x - y}} = \frac{{{{\left( {x - y} \right)}^2}}}{{x - y}} = x - y\\
8)\\
a)\frac{{2x + 4}}{{10}} + \frac{{2 - x}}{{15}} = \frac{{3\left( {2x + 4} \right)}}{{30}} + \frac{{2\left( {2 - x} \right)}}{{30}}\\
= \frac{{6x + 12 + 4 - 2x}}{{30}} = \frac{{4x + 16}}{{30}}\\
= \frac{{2x + 8}}{{15}}
\end{array}$
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