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Math Help - inequality discriminants

  1. #1
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    inequality discriminants

    hi all, the question is: obtain an inequality satisified by k if the equation below has two distinct real roots

    x^2 - 2x - k = 0

    so i made that into 4 - 4k > 0 then

    -4k > -4 then i would presume the final answer is

    k > 1

    but the books answer is k > -1

    why is this? thanks

    Mark
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  2. #2
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    Quote Originally Posted by mark View Post
    hi all, the question is: obtain an inequality satisified by k if the equation below has two distinct real roots

    x^2 - 2x - k = 0

    so i made that into 4 - 4k > 0 then

    -4k > -4 then i would presume the final answer is

    k > 1

    but the books answer is k > -1

    why is this? thanks

    Mark
    You need to add 4k because -4ac = -4*1*-k = +4k

    From there solve to give the book's answer
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  3. #3
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    ha woops, yeah that was a stupid mistake. thanks though
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