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B Help me understand a simple calculation

  1. Mar 4, 2017 #1
    Why is (1 + sqrt(-5) x (1 – sqrt(-5)) equal to 6?
     
  2. jcsd
  3. Mar 4, 2017 #2

    mfb

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    Did you expand the expression?

    Do you know about imaginary numbers? You don't have to to calculate the expression, but it helps understanding what is going on.
     
  4. Mar 4, 2017 #3
    I don't know how to work with imaginary numbers.
     
  5. Mar 4, 2017 #4

    mfb

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    Then just imagine that sqrt(-5) is some number that you don't know. You don't have to use imaginary numbers to solve the problem.
     
  6. Mar 4, 2017 #5
    Typo in my original question - a right bracket is missing. It should be,
    Why is (1 + sqrt(-5)) x (1 – sqrt(-5)) equal to 6?

    Anyone?
     
  7. Mar 4, 2017 #6

    mfb

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  8. Mar 4, 2017 #7
    You just have a difference of squares: (a+b)(a-b) = a^2-b^2 which, in your case means: (1 + sqrt(-5)) (1 – sqrt(-5)) = 1 - (-5)
     
  9. Mar 4, 2017 #8

    berkeman

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    Since Juan has shown the OP how to do this, and the OP keeps refusing to show any effort, this thread is now closed (after some cleanup)
     
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