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Math Help - Systems of Equations with Substitution Method

  1. #1
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    Systems of Equations with Substitution Method

    I have a test tomorrow and I can't figure out why I'm ending up with ridiculous numbers when doing this problem...

    y + 3x = 7
    2x + 3y = 14

    Now I know that you're supposed to work with a variable with a coefficient of 1 because it helps you avoid fractions, so I figure it's best to solve for the "y" in "y + 3x = 7".

    Here's what I'm doing...I'm trying to get the "y" by itself:

    y + 3x = 7
    -3x -3x
    Is this right^? would it be y= 7 - 3x?

    This is only the first step so I might need more help on this.
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  2. #2
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    Quote Originally Posted by endlesst0m View Post
    I have a test tomorrow and I can't figure out why I'm ending up with ridiculous numbers when doing this problem...

    y + 3x = 7
    2x + 3y = 14

    Now I know that you're supposed to work with a variable with a coefficient of 1 because it helps you avoid fractions, so I figure it's best to solve for the "y" in "y + 3x = 7".

    Here's what I'm doing...I'm trying to get the "y" by itself:

    y + 3x = 7
    -3x -3x
    Is this right^? would it be y= 7 - 3x?

    This is only the first step so I might need more help on this.
    Yes, y = 7 - 3x is correct. Using that method, you would then substitute into the second equation:

    2x + 3(7 - 3x) = 14

    2x + 21 - 9x = 14

    2x - 9x = -7

    -7x = -7

    x = 1
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