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Math Help - 3x^2 + mx + 3 = 0, find the value of m

  1. #1
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    3x^2 + mx + 3 = 0, find the value of m

    What is the value of m when -3 is one root of the equation:

    3x^2 + mx + 3 = 0

    Answer key: 10

    Completing squares doesn't seem to work here and (0.5 * m)^2 is not applicable here, how to solve this?

    Thanks.
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  2. #2
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    Quote Originally Posted by shenton View Post
    What is the value of m when -3 is one root of the equation:

    3x^2 + mx + 3 = 0

    Answer key: 10

    Completing squares doesn't seem to work here and (0.5 * m)^2 is not applicable here, how to solve this?

    Thanks.
    You know that: 3(-3)^2-3m+3=0

    Thus: 3(9)-3m+3=0

    Then: 27-3m+3=0

    Therefore: 30-3m=0

    Divide both sides by 3: 10-m=0

    Add m to both sides: \boxed{10=m}
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  3. #3
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    As usual, thanks for showing. Without gurus like you, I would have given up math.
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