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March 30, 2017

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Solve by elimination method. Please show step by step process.
7r-4s=-7
4r+7s=61

  • Math need by 9pm cst - ,

    multiply the top equation by 7, and the bottome equation by 4.
    Then add the equations, which will eliminate the s variable.

    I will be happy to critique your work

  • Math need by 9pm cst - ,

    7r-4s=-7 (7)
    4r+7s=61 (4)

    49r - 28s = -49
    16r + 28s = 244
    ---------------
    65r = 195
    195/65 = 3 (simplified) (3, is the first number of the ordered pair.)

    Now this is the part that I get lost on. I know I am suppose to substitute 3 into one of the equations above, but how do I determine which one. So if I substitute 3 into the 1st equation:

    7(3)-4s= -7
    21 - 4s= -7
    ------------
    21 = -7 would my answer be -7/21

    Substitute 3 into the 2nd equation:

    4(3)+7s = 61
    12 + 7s = 61
    -------------
    12 = 61 would my answer be 61/12

    (3, is the first number of the ordered pair.)

    (3,-7/21) or (3,61/12) which ordered pair is correct?

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