Showing Uniqueness of z^(1/3), z^(1/2) & ln(z) in Complex Plane

In summary, to show that z^{1/3} is not unique in the complex plane, one can write z as re^{i\theta} in polar form and then show that e^{i(\theta+ 2\pi)/3} is not equivalent to e^{i\theta/3} by demonstrating that e^{i(\theta+ 2\pi)}= e^{i\theta}. As for Laurent series, residues, and poles, explanations for these concepts can be found in undergraduate courses and online forums such as the Astrobob Group's website.
  • #1
DanielO_o
7
0
How does one show that z^{1/3} is not unique in the complex plane?

[ Similarly for z^(1/2) and ln(Z) ]


Thanks,

Daniel
 
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  • #2
Write z as [itex]re^{i\theta}[/itex] in "polar form". Then [itex]z^{1/3}= r^{1/3}e^{i\theta/3}[/itex]. Now [itex]e^{i(\theta+ 2\pi)}= e^{i\theta}[/itex] but [itex]e^{i(\theta+ 2\pi)/3}[/itex] is not the same as [itex]e^{i\theta/3}[/itex].
 
  • #3
Thanks :)
 
  • #4
Dear Mentors,

Could anyone include explanations about the Laurent series, & the Residues & Poles ? Everything for an undergraduate course ?

I didn't find anything about that on the forum. if there's a good one please tell me.

Thank You in Advance

----------------
Yours Truly
BOB Merhebi
Astrobob Group
www.astrobob.tk[/URL]
 
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FAQ: Showing Uniqueness of z^(1/3), z^(1/2) & ln(z) in Complex Plane

How do we define the complex numbers z^(1/3), z^(1/2), and ln(z)?

Complex numbers can be represented in the form of a + bi, where a and b are real numbers and i is the imaginary unit (i = √(-1)). The notation z^(1/3) represents the principal cube root of z, z^(1/2) represents the principal square root of z, and ln(z) represents the natural logarithm of z. These functions are defined in the complex plane, where the real part is plotted along the x-axis and the imaginary part is plotted along the y-axis.

How can we show the uniqueness of z^(1/3), z^(1/2), and ln(z) in the complex plane?

To show the uniqueness of these functions, we can use the argument principle, which states that the difference between the number of zeros and poles of a function inside a closed contour is equal to the number of times the function winds around the origin in the counterclockwise direction. By applying this principle to the functions z^(1/3), z^(1/2), and ln(z), we can show that they have unique values in the complex plane.

What are the branch cuts of z^(1/3), z^(1/2), and ln(z)?

The branch cuts of these functions are the lines or curves in the complex plane where the functions are not continuous. For z^(1/3), the branch cut is along the negative real axis; for z^(1/2), the branch cut is along the negative real axis and the origin; and for ln(z), the branch cut is along the negative real axis and the origin. These branch cuts are necessary to define the functions and ensure their uniqueness.

How do we plot z^(1/3), z^(1/2), and ln(z) in the complex plane?

To plot these functions, we can use the argument and modulus representations of complex numbers. The argument of a complex number z is the angle between the positive real axis and the line connecting the origin to z in the complex plane, and the modulus of z is the distance from the origin to z. By varying the argument and modulus of z, we can plot the values of z^(1/3), z^(1/2), and ln(z) in the complex plane.

What are the key properties of z^(1/3), z^(1/2), and ln(z) in the complex plane?

Some key properties of these functions in the complex plane include their non-uniqueness (due to the presence of branch cuts), their multi-valued nature (each function has infinite possible values), and their periodicity (each function repeats its values after a certain interval in the complex plane). Additionally, these functions have different behaviors near the branch cuts and singularities, which can be studied by analyzing their derivatives and Taylor series expansions.

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