quy đồng mẫu số: 3/70; -5/4; 11/20
3/70=6/140
-5/4=-175/140
11/20=77/140
\(\dfrac{3}{70(2)};\dfrac{-5}{4(35)};\dfrac{11}{20(7)}\)
BCNN(70;4;20)=\(2^2 . 5.7\) = 140
\(\dfrac{3}{70}=\dfrac{3.2}{70.2}=\dfrac{5}{140};\dfrac{-5}{4}=\dfrac{(-5).35}{4.35}=\dfrac{-175}{140};\dfrac{11}{20}=\dfrac{11.7}{20.7}=\dfrac{77}{140}.\)