d: \(\Leftrightarrow\left\{{}\begin{matrix}\dfrac{3}{x}-\dfrac{3}{y}=3\\\dfrac{3}{x}+\dfrac{4}{y}=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}-\dfrac{7}{y}=-2\\\dfrac{1}{x}-\dfrac{1}{y}=1\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=\dfrac{7}{2}\\x=\dfrac{7}{9}\end{matrix}\right.\)
f: 2/x-5/y=0
=>2/x=5/y
=>2y=5x
=>y/5=x/2=k
=>y=5k; x=2k
5x+4y=3xy
=>10k+20k=30k2
=>30k^2-30k=0
=>k=1
=>y=5; x=2
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