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Math Help - Factoring Question

  1. #1
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    Factoring Question

    I am asked to factor the equation

    4x^2 - 4x - 15 = 0

    To my knowledge, your supposed to find pairs of factors that multiply to give -15 and add to give -4, correct?

    I can't find a pair that gives both those answers.

    I'm stuck.
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  2. #2
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    Quote Originally Posted by cantstop01 View Post
    I am asked to factor the equation

    4x^2 - 4x - 15 = 0

    To my knowledge, your supposed to find pairs of factors that multiply to give -15 and add to give -4, correct?

    I can't find a pair that gives both those answers.

    I'm stuck.
    4x^2 - 4x - 15 = (2x-5)(2x+3)
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  3. #3
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    Thanks, looks like the answer is x = 5/2 and x = -3/2

    I would like to ask one more thing.

    what is the reasoning behind the factors not actually adding up to -4, yet still being the correct answer?
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  4. #4
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    Quote Originally Posted by cantstop01 View Post
    Thanks, looks like the answer is x = 5/2 and x = -3/2

    I would like to ask one more thing.

    what is the reasoning behind the factors not actually adding up to -4, yet still being the correct answer?
    that "technique" only works if the coefficient of x^2 is 1
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