Bài 3:
a: \(\dfrac{-11}{6}=\dfrac{-11\cdot3}{6\cdot3}=\dfrac{-33}{18};\dfrac{8}{-9}=\dfrac{8\cdot\left(-2\right)}{\left(-9\right)\cdot\left(-2\right)}=\dfrac{-16}{18}\)
mà -33<-16
nên \(\dfrac{-11}{6}< \dfrac{8}{-9}\)
b: \(\dfrac{-25}{20}< 0;0< \dfrac{20}{25}\)
Do đó: \(-\dfrac{25}{20}< \dfrac{20}{25}\)
c: \(\dfrac{15}{21}=\dfrac{15:3}{21:3}=\dfrac{5}{7};\dfrac{21}{49}=\dfrac{21:7}{49:7}=\dfrac{3}{7}\)
mà 5>3
nên \(\dfrac{15}{21}>\dfrac{21}{49}\)
d: \(\dfrac{-19}{49}=\dfrac{-19\cdot47}{49\cdot47}=\dfrac{-893}{49\cdot47}\)
\(\dfrac{-23}{47}=\dfrac{-23\cdot49}{47\cdot49}=\dfrac{-1127}{47\cdot49}\)
mà -893>-1127
nên \(-\dfrac{19}{49}>-\dfrac{23}{47}\)
e: \(\dfrac{998}{555}=\dfrac{555+443}{555}=1+\dfrac{443}{555}\)
\(\dfrac{999}{556}=\dfrac{556+443}{556}=1+\dfrac{443}{556}\)
mà \(\dfrac{443}{555}>\dfrac{443}{556}\left(555< 556\right)\)
nên \(\dfrac{998}{555}>\dfrac{999}{556}\)
f: \(\dfrac{-315}{380}=-1+\dfrac{65}{380};\dfrac{-316}{381}=-1+\dfrac{65}{381}\)
mà \(\dfrac{65}{380}>\dfrac{65}{381}\left(380< 381\right)\)
nên \(-\dfrac{315}{380}>-\dfrac{316}{381}\)
g: \(2020>2018\)
=>\(\dfrac{2020}{2019}>\dfrac{2018}{2019}\)
