\(a.\)

\(\dfrac{-21}{39}=\dfrac{-7\cdot3}{3\cdot13}=-\dfrac{7}{13}\)

\(b.\)

\(-\dfrac{21}{39}=-\dfrac{7}{13}=-\dfrac{14}{26}=\dfrac{-28}{52}=-\dfrac{35}{65}=-\dfrac{42}{78}=-\dfrac{49}{91}\)

\(\)

a) \(-\dfrac{21}{39}=-\dfrac{21:3}{39:3}=-\dfrac{7}{13}\)

b) \(-\dfrac{21}{39}=-\dfrac{7}{13}=-\dfrac{14}{26}=-\dfrac{28}{52}=-\dfrac{35}{65}=-\dfrac{42}{78}=-\dfrac{49}{91}\)

\(\dfrac{14}{21}=\dfrac{7\cdot2}{7\cdot3}=\dfrac{2}{3}\)

\(\dfrac{-36}{48}=\dfrac{-12\cdot3}{12\cdot4}=-\dfrac{3}{4}\)

\(\dfrac{28}{-52}=\dfrac{7\cdot4}{-4\cdot13}=-\dfrac{7}{13}\)

\(\dfrac{-54}{-90}=\dfrac{-18\cdot3}{-18\cdot5}=\dfrac{3}{5}\)

\(\dfrac{14}{21}\) =\(\dfrac{2}{3}\)

\(\dfrac{-36}{48}\) =\(\dfrac{3}{4}\)

\(\dfrac{28}{-52}\)=\(\dfrac{7}{-13}\)

\(\dfrac{-54}{-90}\) =\(\dfrac{6}{9}=\dfrac{2}{3}\)

a: -21/39 rút gọn bằng-7/13

b;-7/13; -42/78

\(-\dfrac{21}{39}=\dfrac{-7}{13}=\dfrac{-42}{78}\)

-21/39=-7/13=-42/78

\(\frac{-21}{39}=\frac{-21:3}{39:3}=\frac{-7}{13}\)

\(\frac{-7}{13}=\frac{-7\cdot2}{13\cdot2}=\frac{-14}{26};\frac{-7}{13}=\frac{-7\cdot3}{13\cdot3}=\frac{-21}{39}\)

\(\frac{-7}{13}=\frac{-7\cdot4}{13\cdot4}=\frac{-28}{52};\frac{-7}{13}=\frac{-7\cdot5}{13\cdot5}=\frac{-35}{65}\)

\(\frac{-7}{13}=\frac{-7\cdot6}{13\cdot6}=\frac{-42}{78};\frac{-7}{13}=\frac{-7\cdot7}{13\cdot7}=\frac{-49}{91}\)

\(\frac{-7}{13}=\frac{-7\cdot8}{13\cdot8}=\frac{-56}{104}\)

Do đó: Các phân số cần tìm là \(\frac{-14}{26};\frac{-21}{39};\frac{-28}{52};\frac{-35}{65};\frac{-42}{78};\frac{-49}{91}\)

\(\dfrac{-21}{39}=\dfrac{-7}{13}=\dfrac{-14}{26}=\dfrac{-28}{52}=\dfrac{-35}{65}=\dfrac{-42}{78}=\dfrac{-49}{91}\)

-21/39=-7/13=-14/26=-21/39=-28/52=-35/65=-42/78=-49/91

đầu tiên ta rút gọn phân số\(\frac{21}{39}\) =

mk tìm đc là \(\frac{42}{78}\)bn nhé

chúc bn hc tốt, nhó k mk nha

 phân số đó là : 42/78

nhớ cho mình 1 tk nha

phân số đó là : 42 / 78

ai đó giúp mình đi

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