xác định a để hệ phương trình
\(\left\{{}\begin{matrix}2x-y=9-3a\\3x+2y=10-a\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}4x-2y=18-6a\\3x+2y=10-a\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}4x-2y+3x+2y=18-6a+10-a\\3x+2y=10-a\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}7x=28-7a\\3x+2y=10-a\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=-a+4\\2y=10-a-3x=10-a-3\left(-a+4\right)\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=-a+4\\2y=10-a+3a-12=2a-2\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=-a+4\\y=a-1\end{matrix}\right.\)
Để x>0 và y>0 thì \(\left\{{}\begin{matrix}-a+4>0\\a-1>0\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}-a>-4\\a>1\end{matrix}\right.\)
=>1<a<4
