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Solving equation with two imaginary roots

  1. Dec 27, 2012 #1
    1. -xn2+2(k+2)x-9k=0
    Has two imaginary roots, what are the values of k?





    Attempted to break it down and use the quadratic formula but wasn't able to do it. Would like a pointer in the right direction of where to begin to solve it.

    Thanks
     
  2. jcsd
  3. Dec 27, 2012 #2

    jedishrfu

    Staff: Mentor

    look at the quadratic formula and ask yourself:

    What is the relationship between the polynomial coefficients to have imaginary roots?
     
  4. Dec 27, 2012 #3

    epenguin

    User Avatar
    Homework Helper
    Gold Member

    Yes, or I could say just look at that quadratic formula and ask yourself what terms must be real (take it that k is real) and what terms can be imaginary, it is a conceptual question not one of calculation.

    Have made one typo? - I suppose that should be maybe

    -x2 + 2(k+2)x -9k= 0

    Check you haven't made another. :wink:
     
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