1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook