a: \(\Leftrightarrow\left\{{}\begin{matrix}3x-4y=2\\10x+4y=28\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}13x=30\\3x-4y=2\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{30}{13}\\4y=3x-2=\dfrac{90}{13}-2=\dfrac{54}{26}=\dfrac{27}{13}\end{matrix}\right.\)
=>x=30/13 và y=27/52
b: \(\Leftrightarrow\left\{{}\begin{matrix}6x-10y=8\\2x-10y=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4x=3\\2x-10y=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=\dfrac{3}{4}\\10y=2x-5=\dfrac{3}{2}-5=-\dfrac{7}{2}\end{matrix}\right.\)
=>x=3/4 và y=-7/20
`{(3x-4y=2), (5x+2y=14):}`
`<=> {(x=30/13), (y=16/13):}`
`{(3x-5y=4), (2x-10y=5):}`
`<=> {(x = 3/4), (y = -7/20):}`