Question

quy đồng mẫu số 

-13/30 và 21/-40

Answer 1

Ta có: 30=2.3.5

40=2³.5

BCNN(30,40)=2³.3.5=120

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

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

Answer 2

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

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

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

Answer 3

\(\dfrac{-13}{30}=\dfrac{-13\times4}{30\times4}=\dfrac{-52}{120};\dfrac{21}{-40}=\dfrac{21\times\left(-3\right)}{-40\times\left(-3\right)}=\dfrac{-63}{120}\)

Answer 4

MSC: 120

\(-\dfrac{13}{30}=-\dfrac{52}{120}\); \(\dfrac{21}{-40}=-\dfrac{63}{120}\)