# How do you solve y=x-4 and y=2x using substitution?

Mar 21, 2016

$x = - 4$
$y = - 8$

#### Explanation:

$y = x - 4$
$y = 2 x$

We know that $y$ is $2 x$ so we replace $y$ in the first equation with $2 x$.

$2 x = x - 4$
$2 x - x = - 4$
$x = - 4$

If $y$ is $2 x$, then $y$=(-4)x2= -8.

$x = - 4$
$y = - 8$