Question

(х+3 у= 5
(2 - x-y= 3

Answer 1

( х + 3у = 5
( 2 - x - y= 3

( х + 3у = 5
( х + у = 2 - 3

( х + 3у = 5
( х + у = -1

Вычтем из первого уравнения второе:
х + 3у - (х + у )= 5 - (-1)
х + 3у - х - у = 6
2у = 6
у = 6 : 2
у = 3

Но
х + у = -1
х + 3 = -1
х = -1 - 3
х = -4

Ответ: х = -4; у =!3

Answer 2

$\[\begin{array}{l}\left\{ \begin{array}{l}x + 3y = 5\\2 - x - y = 3\end{array} \right.\\\\x + 3y + 2 - x - y = 5 + 3,\\2y + 2 = 8,\\2y = 6,\\y = 3.\\\\x + 3 \cdot 3 = 5,\\x = 5 - 9,\\x = - 4.\\\,(x;y) = ( - 4;3)\end{array}\]$