Question

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

Answer 1

• First you regroup them (so that substitution is easier)

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

• Name the equations (again for easier substitution)

`y=3x-9 rarr color(blue)1`
`2y-6x=-18 rarr color(red)2`

• Sub `color(blue)1` in `color(red)2`

`2(3x-9)-6x=-18`

• Then solve

`2(3x-9)-6x=-18`
`6x-18-6x=-18`
`6x-6x=-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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