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Math Help - [SOLVED] equation

  1. #1
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    Aug 2009
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    [SOLVED] equation

    hi, i've got the question-

    find the range of values of the constant c for which the line y = 3x + c does not intersect the parabola with equation y = 2x^2 + 5x - 7

    i know you have to have a discriminant thats less than 0 for this so i strted by putting the equation into one like this 2x^2 + 2x + (-7 - c) so then used the theory : (2)^2 - 4(2)(-7-c) which came to 4 - (- 56 - 8c) which then became (60 - 8c) < 0 then i made it - 8c < - 60 leaving c < 7.5.

    the answer the book gives me is c < - 7.5

    can some explain this please? thanks
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  2. #2
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    Aug 2009
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    ah i just realised, i should have made it + 8c rather than - 8c
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