Estimate ∫γ dz/(1 + z^4) as R→∞.

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In summary, when estimating the integral of dz/(1 + z^4) as R→∞, we can use the residue theorem to simplify the integral into a sum of residues at the poles of the integrand. By considering the behavior of the integrand as R→∞, we can determine which poles are relevant and use the Cauchy residue theorem to evaluate the integral. The end result is an estimation of the integral in terms of the residues at the poles, which can be calculated using the residue formula.
  • #1
blueyellow

Homework Statement



Estimate ∫γ dz/(1 + z^4) as R→∞.

Note that letting z = Re^(it) for t in [0, π]:
|∫γ dz/(1 + z^4)|
= |∫(t = 0 to π) (iRe^(it) dt) / (1 + R^4 e^(4it))|
≤ ∫(t = 0 to π) R dt / |1 + R^4 e^(4it)|
≤ ∫(t = 0 to π) R dt / (R^4 - 1), since R > 1
≤ πR / (R^4 - 1).

but why does iRexp(it)=R ?
why does i exp(it)=1?
please help
 
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  • #2
IT never says that [itex]iRe^{it}=R[/itex]. What you use is that the modulus of that is R. Thus

[tex]|iRe^{it}|=|i||R||e^{it}|=1[/tex]
 

1. What is the purpose of estimating ∫γ dz/(1 + z^4) as R→∞?

The purpose of estimating ∫γ dz/(1 + z^4) as R→∞ is to determine the value of this complex integral as the upper limit of integration approaches infinity (R→∞). This can help in evaluating difficult integrals and understanding the behavior of functions at infinity.

2. How is the integral ∫γ dz/(1 + z^4) related to complex analysis?

The integral ∫γ dz/(1 + z^4) is a common example used in complex analysis to demonstrate the use of contour integration and the Residue Theorem. It also helps in understanding the properties of analytic functions and their behavior in the complex plane.

3. What is the significance of the contour γ in this integral?

The contour γ in this integral represents a closed path in the complex plane, which is used as the path of integration. It can be any closed curve that encloses the poles of the integrand and is chosen to simplify the calculation of the integral.

4. Is there a general approach to estimating ∫γ dz/(1 + z^4) as R→∞?

Yes, there is a general approach to estimating ∫γ dz/(1 + z^4) as R→∞, which involves using the Residue Theorem and the properties of analytic functions. The key steps include identifying the poles of the integrand, calculating the residues at these poles, and then using the Residue Theorem to evaluate the integral.

5. Can this integral be estimated without using complex analysis techniques?

Yes, this integral can also be estimated using traditional calculus techniques. One approach is to split the integral into multiple integrals and use techniques such as partial fractions or trigonometric substitutions to simplify the integrands. However, this may not always be feasible or yield accurate results compared to using complex analysis techniques.

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