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: Quadratic Equations and Completing the Square

  1. Oct 9, 2006 #1
    I am stuck on this problem. I can reach the correct answer with the quadratic formula, but not with the method suggested (completing the square). Thanks in advance.

    The problem is:

    This is what I tried:
    Last edited: Oct 9, 2006
  2. jcsd
  3. Oct 9, 2006 #2
    [tex] 2x^{2} + 8x + 1 = 0 [/tex]. First divide the equation by [tex] 2 [/tex]. So we get: [tex] x^{2} + 4x + \frac{1}{2} = 0 [/tex].

    So [tex] x^{2} + 4x = -\frac{1}{2} [/tex].

    [tex] x^{2} + 4x + 4 = \frac{7}{2} [/tex]
    [tex] (x+2)^{2} = \frac{7}{2} [/tex].
    [tex] x+2 = \sqrt{\frac{7}{2}} [/tex].
    [tex] x = \sqrt{\frac{7}{2}} -2 [/tex].
  4. Oct 9, 2006 #3
    Thanks for the quick reply, but the answer is supposed to end up being

  5. Oct 9, 2006 #4
    [tex] \sqrt{\frac{7}{2}} = \frac{\sqrt{7}}{\sqrt{2}}\frac{\sqrt{2}}{\sqrt{2}} = \frac{\sqrt{14}}{2} [/tex]. It is the same answer. They just rationalized the denominator.
    Last edited: Oct 9, 2006
  6. Oct 9, 2006 #5
    Ohh.. I see. Silly me. Thank you!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook