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

1 Answer
Alan P.
Mar 26, 2016

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#

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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

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