MSC:60 NHA BẠN 

ko bé ơi 

Ta có: 30=2.3.5

40=2³.5

BCNN(30,40)=2³.3.5=120

\(\dfrac{-13}{30}=\dfrac{-13\times4}{30\times4}=\dfrac{-52}{120}\)

\(\dfrac{-21}{40}=\dfrac{-21\times3}{40\times3}=\dfrac{-63}{120}\)

\(-\dfrac{13}{30};\dfrac{21}{-40}\left(MSC=120\right)\)

\(-\dfrac{13}{30}=\dfrac{-13.4}{30.4}=-\dfrac{52}{120}\)

\(-\dfrac{21}{40}=\dfrac{-21.3}{40.3}=-\dfrac{63}{120}\)

Ta có: \(\frac{5}{21}=\frac{5\cdot36}{21\cdot36}=\frac{180}{756}\)

\(\frac{3}{-28}=\frac{-3}{28}=\frac{-3\cdot27}{28\cdot27}=\frac{-81}{756}\)

\(\frac{45}{-108}=\frac{-45}{108}=\frac{-45\cdot7}{108\cdot7}=\frac{-315}{756}\)

12/30 giữ nguyên;13/6=13*5/6*5=65/30

tik nha bạn mình đầu tiên

min moi hoc lop 3 

a: \(\frac{23}{35}<\frac{23,1}{35}=0,66\)

\(0,66=\frac{20,46}{31}<\frac{21}{31}\)

Do đó: \(\frac{23}{35}<\frac{21}{31}\)

b: \(\frac{-17}{24}<\frac{-16}{24}=\frac{-2}{3}\)

\(\frac{-2}{3}=\frac{-13}{19,5}<\frac{-13}{28}\)

Do đó: \(-\frac{17}{24}<-\frac{13}{28}\)

c: \(\frac{9}{16}>\frac{8}{16}=\frac12;\frac12=\frac{12}{24}>\frac{11}{24}\)

Do đó: \(\frac{9}{16}>\frac{11}{24}\)

a)12/21 và 3/21
b)12/36 và 15/36
c)63/56 và 48/56
Chúc bạn học tốt

\(\dfrac{5}{7}=\dfrac{5\times3}{7\times3}=\dfrac{15}{21};\dfrac{6}{21}\)

\(\dfrac{20}{28}=\dfrac{20:4}{28:4}=\dfrac{5}{7};\dfrac{5}{7}\)

5/7=15/21

6/21 giữ nguyên

5/7=20/28 

20/28 giữ nguyên

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