\(\dfrac{2x}{3y}=-\dfrac{1}{3}\Rightarrow\dfrac{2x}{-1}=\dfrac{3y}{3}\)
áp dụng t/c của dãy tỉ số bằng nhau ta có:
\(\dfrac{2x}{-1}=\dfrac{3y}{3}=\dfrac{2x-3y}{-1-3}=\dfrac{7}{-4}\)
\(\dfrac{2x}{-1}=\dfrac{7}{-4}\Rightarrow x=\dfrac{7}{8}\\ \dfrac{3y}{3}=\dfrac{7}{-4}\Rightarrow y=-\dfrac{7}{4}\)
\(\dfrac{2x}{-1}=\dfrac{7}{-4}\Rightarrow2x=\dfrac{7}{-4}.-12x=\dfrac{-7}{-4}\Rightarrow2x=\dfrac{7}{4}\Rightarrow x=\dfrac{7}{4}:2\Rightarrow x=\dfrac{7}{8}\)
\(\dfrac{3y}{3}=\dfrac{7}{-4}\Rightarrow\dfrac{3}{3}.y=\dfrac{7}{-4}\Rightarrow1.y=\dfrac{7}{4}\Rightarrow y=\dfrac{7}{4}\)
Ta có: \(\dfrac{2x}{3y}=-\dfrac{1}{3}\)
nên \(\dfrac{2x}{-1}=\dfrac{3y}{3}\)
mà 2x-3y=7
nên Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:
\(\dfrac{2x}{-1}=\dfrac{3y}{3}=\dfrac{2x-3y}{-1-3}=\dfrac{7}{-4}=-\dfrac{7}{4}\)
Do đó: \(\left\{{}\begin{matrix}2x=\dfrac{7}{4}\\3y=-\dfrac{21}{4}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{7}{8}\\y=-\dfrac{7}{4}\end{matrix}\right.\)