# How do I use substitution to find the solution of the system of equations y=-2x-4 and y+4=-2x?

[1] $y = - 2 x - 4$
[2] $y + 4 = - 2 x$
If you isolate $y$ in [2], the resulting equation is equal to [1]
$y + 4 = - 2 x$
$\implies y = - 2 - 4$
Since [1] is a linear equation, the domain is $\mathbb{R}$. This means that any value of $x$ will yield the same valid value for both equations