Integrating $\tan z$ Around a Circle of Radius 8

In summary, to integrate $\tan z$ around a circle of radius 8, you would need to identify all the singularities and then use the formula $\int_Cf=2\pi i\sum_{n = 1}^m a_i\text{Res}_{z_i}f$, where $a_i = \eta(\gamma,z_i)$ is the winding number. The singularities in a circle of radius 8 centered at z=0 are $\displaystyle z= \pm \frac{\pi}{2}$, $\displaystyle z=\pm \frac{3 \pi}{2}$, and $\displaystyle z=\pm \frac{5 \pi}{2}$. To find the answer, you
  • #1
Dustinsfl
2,281
5
So if I wanted to integrate $\tan z$ around a circle of radius 8, I would need to identify all the singularities and then use
$$
\int_Cf=2\pi i\sum_{n = 1}^m a_i\text{Res}_{z_i}f,
$$
where $a_i = \eta(\gamma,z_i)$ the winding number.
Correct?
 
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  • #2
Yes, that's correct... in case of a circle of course all the singularities have 'winding number' equal to 1...

Kind regards

$\chi$ $\sigma$
 
  • #3
chisigma said:
Yes, that's correct... in case of a circle of course all the singularities have 'winding number' equal to 1...

Kind regards

$\chi$ $\sigma$

So the only singularities would be at $\frac{\pi}{2}$ and $\frac{3\pi}{2}$ or do I have to consider and infinite amount of revolutions?
 
  • #4
In a circle of radius 8 centered in z=0 the singularities are $\displaystyle z= \pm \frac{\pi}{2}$, $\displaystyle z=\pm \frac{3 \pi}{2}$ and $\displaystyle z=\pm \frac{5 \pi}{2}$. Now You have to compute the residue of each singularity, the sum them and finally multiply by $\displaystyle 2 \pi\ i$...

Kind regards

$\chi$ $\sigma$
 
  • #5
chisigma said:
In a circle of radius 8 centered in z=0 the singularities are $\displaystyle z= \pm \frac{\pi}{2}$, $\displaystyle z=\pm \frac{3 \pi}{2}$ and $\displaystyle z=\pm \frac{5 \pi}{2}$. Now You have to compute the residue of each singularity, the sum them and finally multiply by $\displaystyle 2 \pi\ i$...

Kind regards

$\chi$ $\sigma$

So the answer is $-12\pi i$, correct?
 
  • #6
The function $\displaystyle \tan z$ around $\displaystyle z=(2n+1)\ \frac{\pi}{2}$ has the same Laurent expansion of the function $\displaystyle - \cot z$ around $\displaystyle z=0$ so that each residue is - 1 and the result is $\displaystyle - 12\ \pi\ i$...

Kind regards

$\chi$ $\sigma$
 

FAQ: Integrating $\tan z$ Around a Circle of Radius 8

1. How do you integrate $\tan z$ around a circle of radius 8?

To integrate $\tan z$ around a circle of radius 8, you can use the formula $\int_{0}^{2\pi}\tan z dz = -2\pi\ln|e^{i\theta}| \Big|_{0}^{2\pi} = -2\pi\ln|1| - (-2\pi\ln|1|) = 0$. This means that the integral around a full circle is equal to 0.

2. What is the purpose of integrating $\tan z$ around a circle of radius 8?

The purpose of integrating $\tan z$ around a circle of radius 8 is to find the total sum of the function over the entire circle. This can be useful in many applications, such as calculating the total displacement or velocity of an object moving in a circular path.

3. Can you explain the concept of integration around a circle?

Integration around a circle involves finding the value of a function over the entire circumference of a circle. This is done by breaking the circle into smaller sections and finding the sum of the function over each section. As the sections become infinitely small, the sum approaches the value of the integral around the full circle.

4. Are there any special techniques or methods for integrating $\tan z$ around a circle?

Yes, there are special techniques and methods for integrating $\tan z$ around a circle. One method is to use the substitution $u=e^{iz}$, which transforms the integral into a more manageable form. Another technique is to use complex analysis and the Cauchy-Riemann equations to simplify the integration process.

5. Can the concept of integrating around a circle be applied to other functions besides $\tan z$?

Yes, the concept of integrating around a circle can be applied to other functions besides $\tan z$. In fact, it is a common technique used in complex analysis to evaluate integrals of various functions over closed curves. As long as the function is continuous and well-behaved, integration around a circle can be applied.

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