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

1 Answer
Nicolas
Jul 17, 2017
  • 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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