Bài 2:
\(\dfrac{14}{21}=\dfrac{2}{3}=\dfrac{4}{6}\)
\(\dfrac{4}{-12}=\dfrac{-1}{3}=\dfrac{-10}{30}\)
Bài 3:
a: \(-\dfrac{15}{17}=-1+\dfrac{2}{17};\dfrac{-19}{21}=-1+\dfrac{2}{21}\)
mà \(\dfrac{2}{17}>\dfrac{2}{21}\)
nên \(-\dfrac{15}{17}>-\dfrac{19}{21}\)
b: \(-\dfrac{13}{19}=\dfrac{-13\cdot23}{19\cdot23}=\dfrac{-299}{437};\dfrac{19}{-23}=\dfrac{-19}{23}=\dfrac{-19\cdot19}{19\cdot23}=\dfrac{-361}{437}\)
mà -299>-361
nên \(-\dfrac{13}{19}>-\dfrac{19}{23}\)
c: \(-\dfrac{11}{12}< 0;0< \dfrac{7}{9}\)
Do đó: \(-\dfrac{11}{12}< \dfrac{7}{9}\)
d: \(\dfrac{2018}{2019}< \dfrac{2019}{2019}=1;1=\dfrac{18}{18}< \dfrac{19}{18}\)
Do đó: \(\dfrac{2018}{2019}< \dfrac{19}{18}\)
