a) \(BCNN(120;40) = 120\)

\(\frac{11}{120}=\frac{11}{120}\)

\(\frac{7}{40}=\frac{7.3}{40.3}=\frac{21}{120}\)

b) Rút gọn: \({{24} \over {146}} = {{24:2} \over {146:2}} = {{12} \over {73}}\)

\(BCNN(73;13) = 949\)

\({{12} \over {73}}=\frac{12.13}{73.13}=\frac{156}{949}\)

\(\frac{6}{13}=\frac{6.73}{13.73}=\frac{438}{949}\)

c) \(BCNN(30;60;40) = 120\)

\(\frac{7}{30}=\frac{7.4}{30.4}=\frac{28}{120}\)

\(\frac{13}{60}=\frac{13.2}{60.2}=\frac{26}{120}\)

\(\frac{-9}{40}=\frac{-9.3}{40.3}=\frac{-27}{120}\)

d) \(BCNN(60;18;90) = 180\)

\(\frac{17}{60}=\frac{17.3}{60.3}=\frac{51}{180}\)

\(\frac{-5}{18}=\frac{-5.10}{18.10}=\frac{-50}{180}\)

\(\frac{-64}{90}=\frac{-64.2}{90.2}=\frac{-128}{180}\)