# How do you solve the system of linear equations  2x + y = 9 and  x - y = 3?

Feb 17, 2016

$\left(x , y\right) = \left(4 , 1\right)$

#### Explanation:

Given:
[1]$\textcolor{w h i t e}{\text{XXX}} 2 x + y = 9$
[2]$\textcolor{w h i t e}{\text{XXX}} x - y = 3$

Add equations [1] and [2] to get
[3]$\textcolor{w h i t e}{\text{XXX}} 3 x = 12$

Divide equation [3] by $3$
[4]$\textcolor{w h i t e}{\text{XXX}} x = 4$

Substitute $4$ for $x$ in [2]
[5]$\textcolor{w h i t e}{\text{XXX}} 4 - y = 3$

Think about it for a minute, then write
[6]$\textcolor{w h i t e}{\text{XXX}} y = 1$