Giải các hệ phương trình sau bằng phương pháp thế :
a) \(\left\{{}\begin{matrix}4x+5y=3\\x-3y=5\end{matrix}\right.\);
b) \(\left\{{}\begin{matrix}7x-2y=1\\3x+y=6\end{matrix}\right.\);
c) \(\left\{{}\begin{matrix}1,3x+4,2y=12\\0,5x+2,5y=5,5\end{matrix}\right.\);
d) \(\left\{{}\begin{matrix}\sqrt{5}x-y=\sqrt{5}\left(\sqrt{3}-1\right)\\2\sqrt{3}x+3\sqrt{5}y=21\end{matrix}\right.\).
\(\left\{{}\begin{matrix}4x+5y=3\\x-3y=5\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}4\left(5+3y\right)+5y=3\\x=5+3y\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}20+12y+5y=3\\x=5+3y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}20+17y=3\\x=5+3y\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}17y=-17\\x=5+3y\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=-1\\x=2\end{matrix}\right.\)
