Câu 7:
Ta có: \(\dfrac{-9}{15}=\dfrac{-3}{5}.\)
\(\dfrac{6}{-10}=\dfrac{-3}{5}.\\ \dfrac{-15}{25}=\dfrac{-3}{5}\\ \Rightarrow\dfrac{-9}{15}=\dfrac{6}{-10}=\dfrac{-15}{25}.\)
Câu 8:
a/ \(\dfrac{12}{16}=\dfrac{x}{4}=\dfrac{21}{y}=\dfrac{z}{-80}.\)
\(x=3;y=28;z=-60.\)
b/ \(\dfrac{x}{7}=\dfrac{y}{18}=\dfrac{-42}{54}.\Rightarrow\left\{{}\begin{matrix}x=\dfrac{-49}{9}.\\y=-14.\end{matrix}\right.\)
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