# How do you solve y=3x-9 and 2y-6x=-18 using substitution?

Jul 17, 2017
• First you regroup them (so that substitution is easier)

$y = 3 x - 9$
$2 y - 6 x = - 18$

• Name the equations (again for easier substitution)

$y = 3 x - 9 \rightarrow \textcolor{b l u e}{1}$
$2 y - 6 x = - 18 \rightarrow \textcolor{red}{2}$

• Sub $\textcolor{b l u e}{1}$ in $\textcolor{red}{2}$

$2 \left(3 x - 9\right) - 6 x = - 18$

• Then solve

$2 \left(3 x - 9\right) - 6 x = - 18$
$6 x - 18 - 6 x = - 18$
$6 x - 6 x = - 18 + 18$
$0 = 0$

As you may have realised, those simultaenous equations are undefined. Try checking if you got any errors while copying this question.

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