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Homework Help: How do you find the radial value?

  1. Apr 19, 2007 #1
    What is the radial value for the 3rd root of the complex number 4 + -2i ?
     
  2. jcsd
  3. Apr 19, 2007 #2

    J77

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    Did they teach you Euler's formula and De Moivre?
     
  4. Apr 19, 2007 #3
    De Moivre's Theorem
     
  5. Apr 19, 2007 #4

    J77

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    So, you know how to write the complex number in exponential form?
     
  6. Apr 19, 2007 #5
    Can you refresh my memory please?
     
  7. Apr 19, 2007 #6

    J77

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    Euler says that a complex number can be written as [tex]z=re^{i\phi}[/tex], where r is the absolute value of z.

    What is r in your case?
     
  8. Apr 19, 2007 #7
    r = 2 square root of 5?
     
  9. Apr 19, 2007 #8

    J77

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    Yep -- [tex]\sqrt{20}[/tex]. So what's the 3rd root of r?
     
  10. Apr 19, 2007 #9
    that's where im stuck. how do you do that?
     
  11. Apr 19, 2007 #10

    J77

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    De Moivre: [tex]z^n=(re^{i\phi})^n=r^ne^{in\phi}[/tex]
     
  12. Apr 19, 2007 #11
    i'm lost...=/
     
  13. Apr 19, 2007 #12

    J77

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    For the 3rd root, what's n in my previous post?
     
  14. Apr 19, 2007 #13
    it's 3 right?
     
  15. Apr 19, 2007 #14

    J77

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    Nope -- what's a sqaure root expressed as a power?
     
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