What is the Argument of a Complex Number with a Given Modulus?

In summary, z^4= 1/2 + i sqrt(3)/2 can be transformed into polar form as z^4 = e^(i*Pi/3) and the complex root is defined by \sqrt{r e^{i \phi}} = \sqrt{r} e^{i \phi / 2}. By using De Moivre's formula, we get the general solution of z^{1/4} = r^{1/4}*exp(i \phi / 4). Thus, e^((i Pi)/12) is one solution and the other three can be obtained by rotating by 2*pi and so on.
  • #1
kasse
384
1
z^4= 1/2 + i sqrt(3)/2

I start by transforming into polar form:

z^4 = e^(i*Pi/3)

But then I'm blank.
 
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  • #2
kasse said:
z^4= 1/2 + i sqrt(3)/2

I start by transforming into polar form:

z^4 = e^(i*Pi/3)

But then I'm blank.

Have you tried De Moivre's formula ?
 
  • #3
I believe the complex root is defined by (that is: it's usually continued from the real function by)
[tex] \sqrt{r e^{i \phi}} = \sqrt{r} e^{i \phi / 2} [/tex]
 
  • #4
CompuChip said:
I believe the complex root is defined by (that is: it's usually continued from the real function by)
[tex] \sqrt{r e^{i \phi}} = \sqrt{r} e^{i \phi / 2} [/tex]

yes, and from De Moivre's formula we get the general:

[tex] z^{1/n} = r^{1/n}*exp(i \phi / n) [/tex]
 
  • #5
malawi_glenn said:
yes, and from De Moivre's formula we get the general:

[tex] z^{1/n} = r^{1/n}*exp(i \phi / n) [/tex]


So e^((i Pi)/12) is a solution. How about the other three?
 
  • #6
Remember that the same complex number can be obtained by rotating 2*pi and so on.

i.e arg((1/2) + i (rot3 / 2)) = pi / 3 + 2 pi * n, where n is ... -3,-2,-1,0,1,2,3...
 

Related to What is the Argument of a Complex Number with a Given Modulus?

1. What is the definition of the root of a complex number?

The root of a complex number is a number that, when multiplied by itself a certain number of times, gives the original complex number. It is the inverse operation of exponentiation.

2. How do you find the root of a complex number?

To find the root of a complex number, you can use the formula r = a1/n * (cos(θ + 2) + i * sin(θ + 2)), where r is the magnitude of the complex number, a is the base of the root, n is the index of the root, θ is the argument of the complex number, and k is an integer representing the different roots.

3. How many roots does a complex number have?

A complex number has n distinct nth roots, where n is the index of the root. This means that for every complex number, there are n different answers when finding its nth root.

4. What is the principal root of a complex number?

The principal root of a complex number is the root with the smallest positive argument. It is commonly denoted as r1/n, where r is the magnitude of the complex number and n is the index of the root.

5. How is the root of a complex number related to De Moivre's theorem?

The root of a complex number is closely related to De Moivre's theorem, which states that (cos(θ) + i * sin(θ))n = cos() + i * sin(). This theorem can be used to find the roots of a complex number by setting n equal to the index of the root.

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