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Homework Help: Algebra 2

  1. Jul 24, 2010 #1
    1. The problem statement, all variables and given/known data

    Use the disciminant to determine all values of k that would result in the equation x^2 - kx + 4 = 0 having equal roots.

    2. Relevant equations

    x = -b +/- (square root) b^2 - 4ac and divide by 2a

    or b^2 - 4ac

    3. The attempt at a solution

    a = 1
    b = - 1
    c = 4

    I'm a little confused with this problem because instead of a number by b there's a k.
  2. jcsd
  3. Jul 24, 2010 #2


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    Science Advisor

    Which means b is NOT "-1", it is "-k". (That's the whole point of algebra isn't it- that numbers are represented by letters?) The discriminant is, as you say [itex]b^2- 4ac[/itex] which, here, is [itex](-k)^2- 4(1)(4)= k^2- 16[/math].

    Now, in order to have equal roots, what must be true of the discriminant? What values of k make that true?
  4. Jul 24, 2010 #3
    Thanks, i understand now. Therefore, you would have to factor k^2 - 16, (k +4)(k-4), thanks a lot
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