Proving Zero Contour Integral |z-i|=4 traversed once clockwise

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In summary, we can find the integral of 3(z-i)^2 dz around the circle |z-i|=4 by parametrizing the curve in a counterclockwise direction and setting up the integral. Similarly, we can compute the integral of \overline{z} dz around the circle |z|=2 by parametrizing the curve and setting up the integral, making sure to correctly account for the complex conjugate.
  • #1
stunner5000pt
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Find [tex] \int_{C} 3(z-i)^2 dz [/tex] where C is the circle |z-i|=4 traversed once clockwise

well i know it is zero but i just want to prove it.. kind of

so we can parametrize [tex] z(t) = i + 4e^{it}, \ 0\leq t \leq 2 \pi [/tex]

so
[tex] \int_{C} 3(z-i)^2 dz = \int_{0}^{2\pi} 3(i + 4e^{it}-i)^2 (4ie^{it}) dt [/tex]

is the setup good?

Also
Compute [itex] \int_{\Gamma} \overline{z} dz [/tex] where Gamma is the circle |z|=2 tranversed once counterclockwise

[tex] z(t) = 2e^{it} [/tex]
[tex] \int_{0}^{2\pi} (-2e^{it}) (2i e^{it}) dt [/tex]

is this correct??
Thank you for the help!
 
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  • #2
stunner5000pt said:
Find [tex] \int_{C} 3(z-i)^2 dz [/tex] where C is the circle |z-i|=4 traversed once clockwise

well i know it is zero but i just want to prove it.. kind of

so we can parametrize [tex] z(t) = i + 4e^{it}, \ 0\leq t \leq 2 \pi [/tex]

This parameterization is going clockwise, not counterclockwise. Otherwise it looks fine.

stunner5000pt said:
Also
Compute [itex] \int_{Gamma} \overline{z} dz [/tex] where Gamma is the circle |z|=2 tranversed once counterclockwise

[tex] z(t) = 2e^{it} [/tex]
[tex] \int_{0}^{2\pi} (-2e^{it}) (2i e^{it}) dt [/tex]


Check what [tex]\overline{2e^{it}}[/tex] is again.
 

Related to Proving Zero Contour Integral |z-i|=4 traversed once clockwise

1. What is a zero contour integral?

A zero contour integral is a type of line integral in complex analysis that is used to evaluate the integral of a complex-valued function along a closed curve. It is called a zero contour integral because the curve forms a closed loop and the integral evaluates to zero.

2. What does the equation |z-i|=4 mean in the context of the problem?

The equation |z-i|=4 represents a circle with radius 4 centered at the point i in the complex plane. This circle serves as the path for the zero contour integral in the problem.

3. How do you prove that the zero contour integral |z-i|=4 traversed once clockwise evaluates to zero?

To prove that the zero contour integral evaluates to zero, we can use the Cauchy-Goursat theorem, which states that if a function is analytic inside and on a simple closed curve, then the integral of that function around the curve is equal to zero. Since the equation |z-i|=4 represents a simple closed curve, we can use this theorem to show that the zero contour integral evaluates to zero.

4. Are there any other methods to prove the zero contour integral |z-i|=4 traversed once clockwise evaluates to zero?

Yes, there are other methods that can be used to prove the zero contour integral evaluates to zero. One method is to use the Cauchy integral formula, which states that the value of a function at a point inside a simple closed curve can be calculated by integrating the function over the curve. Another method is to use the residue theorem, which states that the value of a function at a point inside a simple closed curve can be calculated by summing the residues of the function at its singular points inside the curve.

5. What are some real-world applications of proving zero contour integrals?

Zero contour integrals have various applications in mathematics, physics, and engineering. In mathematics, they are used to evaluate complex integrals and to prove the fundamental theorem of calculus. In physics, they are used to calculate work done by conservative forces and to analyze electromagnetic fields. In engineering, they are used to analyze circuits and to solve problems related to fluid flow and heat transfer.

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