Câu 7:
a. MC: 75
⇔$\frac{7}{25} = \frac{7*3}{75} = \frac{21}{75}$
$\frac{-4}{15} = \frac{-4*5}{75} = \frac{-20}{75}$
b. MC: 72
⇔$\frac{3}{4} = \frac{3*18}{72} = \frac{54}{72}$
$\frac{1}{9} = \frac{1*8}{72} = \frac{8}{72}$
$\frac{-5}{8} = \frac{-5*9}{72} = \frac{-45}{72}$
c. MC: 4320
⇔$\frac{-54}{90} = \frac{-54*48}{4320} = \frac{-2592}{4320}$
$\frac{180}{288} = \frac{180*15}{4320} = \frac{2700}{4320}$
$\frac{-60}{135} = \frac{-60*32}{4320} = \frac{-1920}{4320}$