Question

 làmmm giúpp e vss

Answer 1

\(\left\{{}\begin{matrix}x-y=1\\3x+y=7\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=1+y\\3\left(1+y\right)+y=7\end{matrix}\right.\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=1+y\\3+3y+y=7\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=1\end{matrix}\right.\)

Answer 2

\(\left\{{}\begin{matrix}x-y=1\left(1\right)\\3x+y=7\left(2\right)\end{matrix}\right.\)

nhân vế `1` với `3`

`=>`\(\left\{{}\begin{matrix}3x-3y=3\left(3\right)\\3x+y=7\left(2\right)\end{matrix}\right.\)

trừ `3` với `2` có :

`3x - 3y - 3x -y = 3 - 7`

`=> -4y = -4`

`=> y = -4 : -4`

`=> y = 1`

thay `y = 1` vào `1` ta đc

`x - 1 = 1`

`=> x = 1+ 1`

`=> x =2`

Vậy `(x,y) = (2,1)`