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Math Help - Elimination method

  1. #1
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    Elimination method

    1) 3(a-b)=9
    2) 4a=b+2

    How do I acheive an ordered pair via the elimination method with this equation??
    Thanks much!
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  2. #2
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    1. a - b = 3, i.e. b = a - 3.
    2. b = 4a - 2
    a - 3 = 4a - 2, i.e. -3 + 2 = 4a - a.
    4a - a = 3a and -3 + 2 = -1, i.e. 3a = -1, hence a = -1/3 and b = -1/3 - 3 = -10/3.
    ∴ (a, b) = (-1/3, -10/3)
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  3. #3
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    Johnny did NOT use the elimination method - he used substitution:

    3(a-b)=9
    4a=b+2

    a - b = 3
    4a - b = 2

    I'm going to multiply the first equation by -1, then add the two equations:

    -a + b = -3
    4a - b = 2

    3a = -1

    a = -1/3

    Now substitute a into either equation to find b.
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