Question

So sánh -7/15 và 20/-39

Answer 1

Ta có: \(-\dfrac{7}{15}=\dfrac{-7\cdot39}{15\cdot39}=-\dfrac{273}{585}\)

\(\dfrac{20}{-39}=-\dfrac{20}{39}=\dfrac{-20\cdot15}{39\cdot15}=-\dfrac{300}{585}\)

Ta có: -273>-300

\(=>-\dfrac{273}{585}>-\dfrac{300}{585}hay-\dfrac{7}{15}>\dfrac{20}{-39}\)

Answer 2

-7 /15 < 20 /(-3)^9

Answer 3

\(\dfrac{-7}{15} ;\dfrac{20}{-39}\) \(= \dfrac{-7}{15};\dfrac{-20}{39}.\)

Sau khi quy đồng ta có :

\(\dfrac{-7}{15}= \dfrac{(-7.)13}{15.13} =\dfrac{-91}{195};\)

\(\dfrac{-20}{39}=\dfrac{20.(-3)}{39.(-3)}=\dfrac{-60}{195}.\)

➩ \(\dfrac{-7}{15}<\dfrac{20}{-39} \) Vì -91> -60