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Understanding Complex number

  1. Apr 14, 2017 #1
    As we know that √-5×√-5=5 i.e multiplication with it self
    My question is that according to this √-1×√-1=1.but it does not hold good in case of i(complex number).
    I.e i^2 =-1. Why???
  2. jcsd
  3. Apr 14, 2017 #2


    Staff: Mentor

    No, this is not true. ##\sqrt{-5} = i\sqrt{5}## so ##\sqrt{-5} \cdot \sqrt{-5} = i^2 (\sqrt{5})^2 = -5##, not 5 as you show above.
    This isn't true, either, for the same reason as above.
    You are apparently using the rule that ##\sqrt a \sqrt b = \sqrt{ab}##. That rule holds only when both a and b are nonnegative real numbers.
  4. Apr 14, 2017 #3
    Thnkuu buddy
  5. Apr 14, 2017 #4


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    Staff: Mentor

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