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Wolfram alpha giving wrong solutions?(link)

  1. Jan 12, 2014 #1
    So yeah, Just using wolfram to help draw a nice function, when this happens:

    http://www.wolframalpha.com/input/?i=x^2/ln(x)

    It shows a real part under zero, when the function given, x^2/ln(x) has no real solution under zero ! It's domain being:

    Dm(f) = ]0;11;infinity[

    need explanations fast.
     
  2. jcsd
  3. Jan 12, 2014 #2

    DrClaude

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    Staff: Mentor

    $$\ln(-x) = \ln(-1 \times x) = \ln(-1) + \ln(x) = i \pi + \ln(x)$$
     
  4. Jan 12, 2014 #3
    This is the imaginary solution.
     
  5. Jan 12, 2014 #4

    Student100

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    I'm confused by the question, but if I understand right what's the of ln(.5), that would give you a negative solution.

    If that's not what you mean select real valued plot, and not complex.
     
  6. Jan 12, 2014 #5
    It shows both the real and complex plot, however the real plot is drawn what seems incorrectly, it should stop at zero since x is not defined under zero for the real solution.
     
  7. Jan 12, 2014 #6

    Borek

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    Staff: Mentor

    Then you don't understand what it shows - blue and red are imaginary and real parts of the complex solution, you have to switch to real valued plot (select it from the drop down).
     
  8. Jan 12, 2014 #7

    Student100

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    It's showing you the real and complex parts of the solution. You need to tab down to real valued plot.
     
  9. Jan 12, 2014 #8
    Ah, that makes sense. Thanks.
     
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