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March 29, 2017

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I'm confused regarding the elimination method for
5x - 7y = -16,
2x + 8y = 26

  • Algebra - ,

    #1: 5x - 7y = -16
    #2: 2x + 8y = 26

    To eliminate y, multiply #1 by 8 and #2 by 7 to get

    40x - 56y = -128
    14x + 56y = 182

    If you add those two new equations, the y's are eliminated and you get

    54x = 54
    x=1

    Now you can go back and calculate y from one of the original equations.

  • Algebra - ,

    5 x - 7 y = - 16 Multiply both sides by - 2

    - 10 x + 14 y = 32


    2 x + 8 y = 26 Multiply both sides by 5

    10 x + 40 y = 130



    - 10 x + 14 y = 32

    10 x + 40 y = 130 Add equations


    - 10 x + 10 x + 14 y + 40 y = 32 + 130

    54 y = 162 Divide both sides by 54

    y = 162 / 54 = 3


    5 x - 7 y = - 16

    5 x - 7 * 3 = - 16

    5 x - 21 = - 16 Add 21 to both sides

    5 x - 21 + 21 = - 16 + 21

    5 x = 5 Divide both sides by 5

    x = 1


    Solutions :

    x = 1 , y = 3

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