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Math Help - Algebra problem

  1. #1
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    Algebra problem

    It says solve by factoring--- x^2 + 2x = 15 I know the answer is x=3 or -5, but I have no idea how to get there by factoring. Any help would be very much appreciated since on the test we will have to show our work.
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  2. #2
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    Quote Originally Posted by onetreehill56 View Post
    It says solve by factoring--- x^2 + 2x = 15 I know the answer is x=3 or -5, but I have no idea how to get there by factoring. Any help would be very much appreciated since on the test we will have to show our work.
    x^2 + 2x - 15 = 0

    List the pairs of factors of -15:
    1, -15
    3, -5
    5, -3
    15, -1

    Which of these add to 2? 5 + (-3) = 2. So
    x^2 + 2x - 15 = 0

    x^2 + 5x - 3x - 15 = 0

    (x^2 + 5x) + (-3x - 15) = 0

    x(x + 5) - 3(x + 5) = 0

    (x - 3)(x + 5) = 0

    -Dan
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  3. #3
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    Factored

    x^2+2*x-15=0 can be factored into (x+5)*(x-3)
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