More of a math problem, but from a physics text

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SUMMARY

The discussion centers on a physics problem involving the transition from line (53) to line (54) in a mathematical expression. Participants clarify that the imaginary part of the integral can be disregarded by recognizing that the final answer is real, thus confirming that the sine terms can be ignored. The use of the identity eiθ = cos(θ) + i*sin(θ) and the properties of even functions, specifically cos(-θ) = cos(θ), are crucial for understanding this transition. The conclusion emphasizes the importance of not overthinking the problem and focusing on the characteristics of the functions involved.

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  • Understanding of complex numbers and Euler's formula (eiθ = cos(θ) + i*sin(θ))
  • Knowledge of even and odd functions in mathematics
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  • Basic grasp of real and imaginary components in mathematical expressions
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  • Study the properties of even and odd functions in depth
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  • Explore techniques for simplifying integrals involving complex numbers
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Students in physics and mathematics, particularly those tackling complex integrals and seeking clarity on the behavior of real and imaginary components in equations.

David92
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Homework Statement

Screen Shot 2017-02-11 at 5.38.35 PM.png
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So I can't get from line (53) to line (54)

I do not understand how interchanging the variables will cause the imaginary part to disappear

The Attempt at a Solution


I'm not sure where to start
I know exp(ix) = cos(x) +isin(x)
And the only way i see cos(x) coming out is using the exponential identity
exp(ix) + exp(-ix) = 2cos(x) (but this clearly isn't it)
But this 'interchanging' variables really doesn't make sense to me
Please help! The answer is apparently obvious! haha
 
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David92 said:

Homework Statement

View attachment 113014 [/B]
So I can't get from line (53) to line (54)
From the identity e = cos(θ)+i*sin(θ), you can split the real and imaginary parts of the integral. You also know that the cosine is an even function, so cos(-θ) = cos(θ) is used to remove the negative exponent.
I do not understand how interchanging the variables will cause the imaginary part to disappear
You are over-thinking it. That is not what makes the imaginary part disappear. If you know that the final answer is real, then you know that the imaginary part is zero without having to do anything. So just ignore the sin terms.
 
Last edited:
Oh wow you are right I was overthinking it. Thinking in terms of even and odd functions really helped, thanks!
 

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