$\text{Theo như đề bài ta có:}$
$\dfrac{-1}{2}$;$\dfrac{0}{7}$;$\dfrac{-1}{5}$;$\dfrac{-1}{-4}$ $\text{MSC:140}$ $\text{TSP:70;20;28;35}$
$\text{Vì$\dfrac{-1}{-4}$=$\dfrac{1}{4}$nên mới có TSP=15 mà không phải là -15}$
$\text{Ta có:}$
$\text{$\dfrac{-1}{2}$=$\dfrac{(-1.)70}{2.70}$=$\dfrac{-70}{140}$}$
$\text{$\dfrac{0}{7}$=$\dfrac{0.20}{7.20}$}$=$\dfrac{0}{140}$
$\text{$\dfrac{-1}{5}$=$\dfrac{(-1).28}{5.28}$=$\dfrac{-28}{140}$}$
$\text{$\dfrac{-1}{-4}$=$\dfrac{1.35}{4.35}$=$\dfrac{35}{140}$}$
$\text{$\Rightarrow$$\dfrac{-70}{140}$<$\dfrac{-28}{140}$<$\dfrac{0}{140}$,$\dfrac{35}{140}$}$
$\text{$\dfrac{-1}{-4}$lớn nhất}$
