Understanding Complex Numbers: Find the Answer

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Discussion Overview

The discussion revolves around the properties and calculations involving complex numbers, specifically the imaginary unit \( i \) and its powers. Participants explore the confusion surrounding the expression \( i^3 \) and the notation related to square roots of negative numbers. The scope includes conceptual clarification and mathematical reasoning.

Discussion Character

  • Conceptual clarification
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant claims that \( i^3 \) should equal \( i \) based on their interpretation of the square root of negative one, leading to confusion.
  • Another participant asserts that \( i^3 \) is correctly calculated as \( -i \) and challenges the notation used by the first participant.
  • Some participants express unfamiliarity with Euler's constant and complex calculus, indicating a need for further explanation.
  • A participant points out a mistake in the manipulation of square roots of negative numbers, emphasizing that the property \( \sqrt{a}\sqrt{b}=\sqrt{ab} \) does not hold when both \( a \) and \( b \) are negative.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the interpretation of \( i \) and its powers, with multiple competing views presented regarding the correct calculation of \( i^3 \) and the use of square roots of negative numbers.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the properties of square roots and the notation used, which may lead to misunderstandings. The discussion also reflects varying levels of familiarity with complex numbers and related concepts.

kay
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We know that i^3 is -i .
But I am getting confused, because I thought that i can be written as √(-1) and i^3 = √(-1) × √(-1) × √(-1) = √(-1 × -1 × -1) = √( (-1)^2 × -1) = √(1× -1) = √(-1) = i
( and not -i ).
Please help.:rolleyes:
Sorry I couldn't use superscript because I was using my phone.
 
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https://www.physicsforums.com/showthread.php?t=637214
 
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i definitely is not \sqrt{-1}. If you like (abuse of notation)
\sqrt{-1} = \pm i
Using (this not correct notation) \sqrt{-1}^3 = \pm i. Much better is of course
i^3 = (i*i)*i = -1*i = -i
 
micromass said:
https://www.physicsforums.com/showthread.php?t=637214
i am really not familiar with Euler's constant that much, and complex calculus, but thanks. :)
 
Last edited by a moderator:
dieterk said:
i definitely is not \sqrt{-1}. If you like (abuse of notation)
\sqrt{-1} = \pm i
Using (this not correct notation) \sqrt{-1}^3 = \pm i. Much better is of course
i^3 = (i*i)*i = -1*i = -i

I didn't understand anything. :|
 
kay said:
i am really not familiar with Euler's constant that much, and complex calculus, but thanks. :)


The link given by micromass has everything you need to know and you don't need to know Euler's Formula to understand what he meant. I suggest read (not skim) the link provided by micromass.
 
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When you got to this point: $$\sqrt{-1}\cdot\sqrt{-1}\cdot\sqrt{-1}=\sqrt{(-1)\cdot(-1)\cdot(-1)},$$ you made a mistake since [itex]\sqrt{a}\sqrt{b}=\sqrt{ab}[/itex] isn't true when [itex]a,b\lt0[/itex].
 

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