Question

How do you solve `9x+7y = -65` and `x= -1-7y` using substitution?

Answer 1

Given
[1]`color(white)("XXX")9x+7y=-65`
[2]`color(white)("XXX")x=-1-7y`

By substitution
Substituting `(-1-7y)` from [2] into [1] for `x`
[3]`color(white)("XXX")9(-1-7y)+7y=-65`
Simplifying
[4]`color(white)("XXX")-9-63y+7y=-65`

[5]`color(white)("XXX")-56y=-56`

[6]`color(white)("XXX")y=1`

Substituting `1` from [6] into [2] for `y`
[7]`color(white)("XXX")x=-1-7(1)`
Simplifying
[8]`color(white)("XXX")x=-8`

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Verify by substituting `(x,y)=(-8,1)` into equation [1]