How do you solve the system 3x+y=12 and y=-x-2 using substitution?

Sep 29, 2017

$x = 7$
$y = 9$

Explanation:

From the second equation you know what y is equal to. You can substitute this into the first equation.

$3 x + \left(- x - 2\right) = 12$

$3 x - x - 2 = 12$

$3 x - x = 12 + 2$

$2 x = 14$

$x = 7$

Now we can substitute our value of x into the second equation to find y.

$y = - \left(7\right) - 2$

$y = - 7 - 2$

$y = - 9$