+118723 $$\\\frac{-2}{7}=\frac{-2*2}{7*2}=\frac{-4}{14}\\\\
\frac{-1}{2}=\frac{-1*7}{2*7}=\frac{-7}{14}\\\\
\mbox{so compare }\frac{-4}{14}\; \;\;\frac{-7}{14}\\\\$$
here you can see that
$$\quad -4>-7\\\\
therefore\quad \frac{-4}{14}>\frac{-7}{14}\\\\
therefore\quad \frac{-2}{7}>\frac{-1}{2}\\\\$$
+118723 $$\\\frac{-2}{7}=\frac{-2*2}{7*2}=\frac{-4}{14}\\\\
\frac{-1}{2}=\frac{-1*7}{2*7}=\frac{-7}{14}\\\\
\mbox{so compare }\frac{-4}{14}\; \;\;\frac{-7}{14}\\\\$$
here you can see that
$$\quad -4>-7\\\\
therefore\quad \frac{-4}{14}>\frac{-7}{14}\\\\
therefore\quad \frac{-2}{7}>\frac{-1}{2}\\\\$$
