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!

Best ways in solving cubic equations without information on roots

  1. Oct 5, 2012 #1
    1. The problem statement, all variables and given/known data

    Learning to solve cubic equations without the knowledge of any roots, and the easiest way I found out so far is still time-consuming :grumpy:

    2. Relevant equations

    The equation and attempt is shown in the image below, tell me if its unclear :shy:

    3. The attempt at a solution

    http://sphotos-a.ak.fbcdn.net/hphotos-ak-prn1/c67.0.403.403/p403x403/60637_450846098287003_1194154338_n.jpg [Broken]

    eventually found out x=7. Then by reducing the equation into a quadratic, I can find the other roots

    So are there better ways in solving cubic? maybe some hacking fast ones? :D Appreciate the help! :rofl:
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 5, 2012 #2

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    You should try to find a rational root first using the Rational Root theorem. If you can find one, then you are practically done. Only if there aren't any would I resort to your technique.
     
  4. Oct 9, 2012 #3

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    In fact, doing that, it is easy to find three small integer roots.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Best ways in solving cubic equations without information on roots
  1. Cubic equation roots (Replies: 5)

Loading...