a.Ta có:\(\dfrac{1691}{3259}< \dfrac{1691}{1234}\)
mà \(\dfrac{1691}{1234}< \dfrac{1785}{1234}\)
→\(\dfrac{1691}{3259}< \dfrac{1785}{1234}\)
b) Ta có: \(\dfrac{2761}{3594}< 1\)
\(1< \dfrac{4181}{1312}\)
Do đó: \(\dfrac{2761}{3594}< \dfrac{4181}{1312}\)
\(\Leftrightarrow\dfrac{-2761}{3594}>\dfrac{-4181}{1312}\)

