Question

Cho hệ phương trình `{(x+y=3),(x-y=m):}` có nghiệm `(x;y)=(2;1)` khi

Answer 1

\(\Leftrightarrow\left\{{}\begin{matrix}2+1=3\\2-1=m\end{matrix}\right.\Leftrightarrow m=1\)

Answer 2

\(\left\{{}\begin{matrix}x+y=3\\x-y=m\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2+1=3\\2-1=m\end{matrix}\right.\Leftrightarrow}\left\{{}\begin{matrix}3=3\\m=1\end{matrix}\right.\)