\(a,\dfrac{x}{3}=\dfrac{7}{y}\Rightarrow x.y=3.7=21\\ =1.21=21.1\)
vậy nếu \(x=1\) thì \(y=21\)
\(x=21\) thì \(y=1\)
\(b,\dfrac{-3}{x}=\dfrac{y}{5}\Rightarrow\left(-3\right).5=x.y=-15\\ =\left(-1\right).15=1.\left(-15\right)\)
vậy nếu \(x=-1\) thì \(y=15\)
\(x=1\) thì \(y=-15\)
\(c,\dfrac{x}{y}=\dfrac{1}{6}\Rightarrow y=6x\left(x\in Z\right)\)
thì \(y=6Z\) → x, y vô số
\(d,\dfrac{x}{7}=\dfrac{y}{-3}\Rightarrow-3x=7y\\ \Rightarrow\dfrac{7x}{-3}\)
để \(x\in Z\Rightarrow y:3\)
vậy \(y=3a\left(a\in Z\right)\\ th\text{ì}x=-7a\)
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