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How do you solve the following system: #x-5y=-9, y = 3x – 12#?

1 Answer

Mar 26, 2018

You have to substitute (replace) one of the unknowns into the other equation

Explanation:

We know that #x-5y=-9#, so from here we have:

#x=5y-9#. Substituting in the other equation we have:

#y=3x-12=3(5y-9)-12=15y-27-12=15y-39#, and then:

#y+39=15y#, and so #39=14y#, and then #y=39/14#

We can now use that #x=5y-9#, so we have #x=5*39/14-9=195/14-9=(195-126)/14=69/14#

The solutions are then #x=69/14, y = 39/14#

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