Đáp án: D
Giải thích các bước giải:
$\begin{array}{l}
\dfrac{{x - y}}{3} = \dfrac{{x + y}}{{13}} = \dfrac{{x.y}}{{80}}\\
= \dfrac{{x - y + x + y}}{{3 + 13}} = \dfrac{{2x}}{{16}} = \dfrac{x}{8}\\
\Leftrightarrow \dfrac{{x.y}}{{80}} - \dfrac{x}{8} = 0\\
\Leftrightarrow x.y - 10x = 0\\
\Leftrightarrow x.\left( {y - 10} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = 0 \Leftrightarrow y = 0\\
y = 10 \Leftrightarrow \dfrac{{x - 10}}{3} = \dfrac{{x.10}}{{80}} \Leftrightarrow x = 16
\end{array} \right.\\
\Leftrightarrow \left( {x;y} \right) \in \left\{ {\left( {0;0} \right);\left( {16;10} \right)} \right\}
\end{array}$
