# How do you solve by substitution x-y+-15 and x+y=-5?

Jun 5, 2015

Assuming the first component should have ($= -$) instead of ($\pm$)

[1]$\textcolor{w h i t e}{\text{XXXX}}$$x - y = - 15$
[2]$\textcolor{w h i t e}{\text{XXXX}}$$x + y = - 5$

Rearranging the terms of [1]
[3]$\textcolor{w h i t e}{\text{XXXX}}$$x = y - 15$

Substituting $\left(y - 15\right)$ for $x$ into [2]
[4]$\textcolor{w h i t e}{\text{XXXX}}$$\left(y - 15\right) + y = - 5$
[5]$\textcolor{w h i t e}{\text{XXXX}}$$y = 5$

Substituting $5$ for $y$ back in [1]
[6]$\textcolor{w h i t e}{\text{XXXX}}$$x - 5 = - 15$
[7]$\textcolor{w h i t e}{\text{XXXX}}$$x = - 10$

Solution: $\left(x , y\right) = \left(- 10 , 5\right)$