a) \({{ - 5} \over 5},{8 \over 7}\)

Ta có: \(\frac{-5}{5}=-1=\frac{-7}{7}\)

Quy đồng ta được hai phân số: \(\frac{-7}{7}\) và \(\frac{8}{7}\)

b) \(3,{{ - 3} \over 5},{{ - 5} \over 6}\)  MSC 30

\(3=\frac{3.30}{30}=\frac{90}{30}\)

\(\frac{-3}{5}=\frac{-3.6}{5.6}=\frac{-18}{30}\)

\(\frac{-5}{6}=\frac{-5.5}{6.5}=\frac{-25}{30}\)

c) \({{ - 9} \over 7},{{ - 19} \over {15}}, - 1\)  MSC $7.15=105$

\(\frac{-9}{7}=\frac{-9.15}{7.15}=\frac{-135}{105}\)

\(\frac{-19}{15}=\frac{-19.7}{15.7}=\frac{-133}{105}\)

\(-1=\frac{-105}{105}\)