a: \(\left\{{}\begin{matrix}3x-y=5\\5x+2y=28\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}6x-2y=10\\5x+2y=28\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}11x=38\\3x-y=5\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=\dfrac{38}{11}\\y=3x-5=3\cdot\dfrac{38}{11}-5=\dfrac{114}{11}-5=\dfrac{59}{11}\end{matrix}\right.\)
b: \(\left\{{}\begin{matrix}2x+y=3\\x+3y=4\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}6x+3y=9\\x+3y=4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}5x=5\\x+3y=4\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=1\\3y=4-x=4-1=3\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=1\\y=1\end{matrix}\right.\)
c: \(\left\{{}\begin{matrix}3x+5y=1\\2x-y=-8\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}3x+5y=1\\10x-5y=-40\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}13x=-39\\2x-y=-8\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=-3\\y=2x+8=2\cdot\left(-3\right)+8=2\end{matrix}\right.\)
d: \(\left\{{}\begin{matrix}x-3y=5\\3x+4y=2\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}3x-9y=15\\3x+4y=2\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}-13y=13\\x-3y=5\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}y=-1\\x=3y+5=3\cdot\left(-1\right)+5=5-3=2\end{matrix}\right.\)
