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Beware the complex number

  1. Mar 31, 2004 #1
    [tex] 4 = \sqrt {4*4} = \sqrt {4*4*i^4} =\sqrt {i^2*4 *4*i^2} [/tex]

    [tex] = i\sqrt{4}*i\sqrt{4} =2i*2i =-4[/tex]

    this is wrong but which setp
    =)
     
  2. jcsd
  3. Mar 31, 2004 #2
    You don't even have to go through that much work.

    [tex]4 = \sqrt{16} = -4[/tex]

    cookiemonster
     
  4. Mar 31, 2004 #3
    That should be:
    [tex]4 = |\sqrt {4*4}| = |\sqrt {4*4*i^4}| = |\sqrt {i^2*4 *4*i^2}|[/tex]
    [tex] = |i\sqrt{4}*i\sqrt{4}| = |2i*2i| = |-4|[/tex]
    Or just:
    [tex]4 = |\sqrt{16}| = |-4|[/tex]
     
  5. Mar 31, 2004 #4
    hehe oh? i was told that it sippose to be wrong
    in somewhere that i forgot.
     
  6. Mar 31, 2004 #5
    Well, it's wrong in that you're taking the wrong sign in front of the square root, but that's about it. Squares and square roots tend to generate extra solutions that are not necessarily correct. This is one such case.

    cookiemonster
     
  7. Mar 31, 2004 #6
    yep i agree, i remmber now haha
     
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