Ta có: \(\dfrac{-12}{15}=\dfrac{-4}{5}\); \(\dfrac{ -15}{20}=\dfrac{-3}{4}\);
\(\dfrac{ 24}{-32}=\dfrac{3}{-4}=\dfrac{-3}{4}\); \(\dfrac{ -20}{28}=\dfrac{-5}{7}\);
\(\dfrac{ -27}{36}=\dfrac{-3}{4}\); \(\dfrac{ 3}{-4}=\dfrac{-3}{4}\)
Suy ra \(\dfrac{ -15}{20}=\dfrac{ 24}{-32}=\dfrac{ -27}{36}=\dfrac{ 3}{-4}=\dfrac{-3}{4}\)
So sánh: \(\dfrac{-3}{4}\) và \(\dfrac{-4}{5}\) và \(\dfrac{-5}{7}\)
Ta có: \(\dfrac{-3}{4}=\dfrac{-60}{80}\);
\(\dfrac{-4}{5}=\dfrac{-60}{75}\);
\(\dfrac{-5}{7}=\dfrac{-60}{84}\);
Do \(\dfrac{60}{75}>\dfrac{60}{80}>\dfrac{60}{84}\)
suy ra \(\dfrac{-60}{75}<\dfrac{-60}{80}<\dfrac{-60}{84}\)
suy ra \(\dfrac{-4}{5}<\dfrac{-3}{4}<\dfrac{-5}{7}\)
suy ra \(\dfrac{-12}{15}<\dfrac{ -15}{20}=\dfrac{ 24}{-32}=\dfrac{ -27}{36}=\dfrac{ 3}{-4}<\dfrac{-20}{28}\)
Vậy ta có hình vẽ biểu diễn
