De moivre's theorem complex number

In summary, the conversation discusses the equation (a+b)c = ac+bc and how it relates to complex numbers and DeMoivre's Theorem. However, it is actually just the distributive law and has a connection to Morrie's Law, which was a concept mentioned by physicist Richard Feynman in his childhood. This equation has practical applications in geometry and specifically in the proof of Urquhart's Theorem.
  • #1
kelvin macks
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can anyone explain how ro make the working above the red circle to the working in the red circle? why the author do this?
 

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  • #2
It's equivalent to having

(a+b)c = ac+bc

where

[tex]a=z^2+\frac{1}{z^2}[/tex]

[tex]b=2[/tex]

[tex]c=z^2-\frac{1}{z^2}[/tex]

and why he did it should be pretty evident from his next two lines.
 
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  • #3
It has nothing to do with "complex numbers" or "DeMoivre's Theorem". It is, as mentallic said, just the distributive law.
 
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  • #4
Hahaha, this is something Feynman talked about from his childhood. What you've presented is actually a higher-order form of something called Morrie's[/PLAIN] Law (Feynman's little friend in childhood). From what I've studied, a useful application is in the proof of http://2000clicks.com/MathHelp/GeometryTriangleUrquhartsTheorem.aspx.
 
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  • #5


De Moivre's theorem is a mathematical theorem that relates to complex numbers. It states that for any complex number z and any integer n, the n-th power of z can be expressed as the product of z and its complex conjugate raised to the n-th power.

The working above the red circle likely refers to the steps leading up to the application of De Moivre's theorem, while the working in the red circle refers to the actual application of the theorem. This is likely done in order to simplify the problem and make it easier to solve.

The reason why the author chose to use De Moivre's theorem in this particular problem may be because it allows for a more efficient and elegant solution. By using the theorem, the author can avoid lengthy calculations and instead use the properties of complex numbers to find the solution. Additionally, De Moivre's theorem has many practical applications in fields such as physics, engineering, and economics, making it a useful tool for problem-solving.
 

Related to De moivre's theorem complex number

1. What is De Moivre's theorem for complex numbers?

De Moivre's theorem for complex numbers states that for any complex number, the nth power of the number can be found by raising its modulus (or absolute value) to the power of n and multiplying it by the cosine of n times the argument (or angle) of the complex number, plus i times the sine of n times the argument.

2. How is De Moivre's theorem used in mathematics?

De Moivre's theorem is used in mathematics to simplify calculations involving complex numbers. It allows us to easily find the powers of complex numbers, which can be useful in solving equations and simplifying expressions.

3. What is the significance of De Moivre's theorem in the study of trigonometry?

De Moivre's theorem is significant in trigonometry because it provides a way to express complex numbers in terms of trigonometric functions. This allows us to use techniques from trigonometry to solve problems involving complex numbers.

4. Can De Moivre's theorem be extended to non-integer powers?

Yes, De Moivre's theorem can be extended to non-integer powers. This is known as the complex exponential function and is defined as e raised to the power of the complex number. It follows the same pattern as De Moivre's theorem, but allows for non-integer powers.

5. How is De Moivre's theorem related to Euler's formula?

De Moivre's theorem is related to Euler's formula through the use of complex numbers. Euler's formula states that e to the power of i times the argument of a complex number is equal to the cosine of the argument plus i times the sine of the argument. This is similar to De Moivre's theorem, where the power of the complex number is equal to the cosine of the argument plus i times the sine of the argument.

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