a. \(\left\{{}\begin{matrix}4x-3y=-10\\2x+5y=8\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4x-3y=-10\\4x+10y=16\end{matrix}\right.\)
Trừ vế cho vế:
\(\Leftrightarrow-13y=26\)
\(\Leftrightarrow y=2\)
Thay y = 2 vào 2x + 5y = 8 ta được:
\(2x+5\cdot2=8\Leftrightarrow x=-1\)
Vậy \(\left(x;y\right)=\left(-1;2\right)\)
b. \(\left\{{}\begin{matrix}5x+3y=19\\2x+9y=31\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}10x+6y=38\\10x+45y=155\end{matrix}\right.\)
Trừ vế cho vế:
\(\Leftrightarrow-39y=-117\Leftrightarrow y=3\)
Thay y = 3 vào 2x + 9y = 31 ta được:
\(2x+9\cdot3=31\Leftrightarrow x=2\)
Vậy \(\left(x;y\right)=\left(2;3\right)\)
