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Math Help - square root of -1

  1. #1
    Member u2_wa's Avatar
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    square root of -1

    Here is the mcq:

    \sqrt{-1}*\sqrt{-1}=

    a) -1

    b) 1 [ \sqrt{-1*-1}]

    c) both of a & b

    Thanks in advance
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  2. #2
    Junior Member piglet's Avatar
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    Quote Originally Posted by u2_wa View Post
    Here is the mcq:

    \sqrt{-1}*\sqrt{-1}=

    a) -1

    b) 1 [ \sqrt{-1*-1}]

    c) both of a & b

    Thanks in advance
    I would say a)  -1 . I was always taught that when multiplying two square roots together, the answer is what ever is under the square root sign i.e.  \sqrt{2}*\sqrt{2} = 2
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  3. #3
    MHF Contributor undefined's Avatar
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    Using imaginary numbers,

    \sqrt{-1}\cdot\sqrt{-1}=i\cdot i=-1.
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  4. #4
    MHF Contributor
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    TRY the darn thing on something easy; like:
    sqrt(4) * sqrt(4)
    = 2 * 2
    = 4
    Kapish?
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  5. #5
    Junior Member piglet's Avatar
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    Quote Originally Posted by Wilmer View Post
    TRY the darn thing on something easy; like:
    sqrt(4) * sqrt(4)
    = 2 * 2
    = 4
    Kapish?
    Everything except kapish...
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  6. #6
    A riddle wrapped in an enigma
    masters's Avatar
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    And...

    \sqrt{-1} \cdot \sqrt{-1}=(-1)^{\frac{1}{2}} \cdot (-1)^{\frac{1}{2}}=(-1)^{\frac{1}{2}+\frac{1}{2}}=(-1)^1=-1
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