1. Not finding help here? Sign up for a free 30min 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!

Sounds simple enough

  1. May 1, 2014 #1

    Atomised

    User Avatar
    Gold Member

    1. The problem statement, all variables and given/known data

    I am asked to solve the following equation, giving answer in terms of k

    2. Relevant equations

    $$x^5 + k^2x = 0$$

    3. The attempt at a solution

    The answer is apparently 0. What is 0. Not even sure what that means.

    I would have thought: divide through by x to obtain

    $$k^2 = -x^4$$ →

    $$ k=x^2i $$ ???
     
  2. jcsd
  3. May 1, 2014 #2
    You solved for k. I think you were supposed to solve for x.

    I agree with you that there is more than one root.
     
    Last edited: May 1, 2014
  4. May 1, 2014 #3

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Dividing both sides of an equation by anything except zero, gives you an equivalent equation.

    You can divide by x, as long as it's not equal to zero.
    What if x is zero?

    Evaluate that case another way, for instance, by plugging zero in for x.​
     
  5. May 1, 2014 #4

    Mark44

    Staff: Mentor

    The "answer" is not zero. Your answer should be in the form of equations that start with "x = ..."

    One of the solutions is x = 0, but there is another. Factoring the left side would be helpful.
     
  6. May 1, 2014 #5

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    You have committed the worst sin in mathematics, viz., dividing by x before checking that it is allowed. If x = 0 you cannot do any such division---but in that case, you don't need to anyway. If x ≠ 0 then---and only then---can you divide both sides by x.
     
  7. May 2, 2014 #6

    Atomised

    User Avatar
    Gold Member

    Thanks Mark & Ray for these lessons - a great help in learning to think properly.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Sounds simple enough
  1. Sound loudness (Replies: 1)

  2. Simple Algebra (Replies: 12)

  3. A simple qestion (Replies: 7)

Loading...