Elementary exponential integral

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Discussion Overview

The discussion revolves around the evaluation of the integral \(\int e^{i2t} dt\) from 0 to \(t\). Participants explore various methods for solving the integral, including substitution and comparisons to similar integrals, while addressing potential issues with variable naming and integration techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant requests help with the integral \(\int e^{i2t} dt\) and expresses confusion over using trigonometric identities.
  • Another suggests using a u-substitution with \(u=2it\) and \(du=2i dt\) as a potential method for solving the integral.
  • A participant questions the necessity of substitution, arguing that the integral resembles \(\int_0^t e^{at}\,dt\) where \(a\) is a complex number.
  • Concerns are raised about using the same variable in both the bounds and the integrand, suggesting it may be better to use a different variable like \(\tau\).
  • A participant relates the integral to the expression \(\int_0^t e^{-2i\tau}d\tau\) and mentions an expected result involving \(\cos\), but expresses difficulty in reaching that result.
  • Another participant questions whether it is the integral or the integrand that is squared in the context of the discussion.
  • A claim is made regarding the evaluation of the integral \(\int_0^t e^{-2i\tau}d\tau\), providing a specific result, while challenging the previously mentioned expected result involving \(\cos\).

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to evaluate the integral, and multiple competing views and methods are presented throughout the discussion.

Contextual Notes

There are unresolved issues regarding variable naming in the integration bounds and the integrand, as well as differing interpretations of the expected results from the integrals discussed.

Master J
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I'm sure this integral is easy, but could someone perhaps show the working of:

[tex]\int[/tex] e[tex]^{i2t}[/tex] dt between t and 0.

I've tried it with trigonometric identities and keep getting lost!

Cheers!
 
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Try a u-substitution.

u=2it
du=2i dt
 
Why do you need to do a substitution?

It is exactly the same as

[tex]\int_0^t e^{at}\,dt[/tex]

except that [tex]a[/tex] is a complex number.
 
Although strictly speaking, it's bad form to use the same variable in your bounds and your integrand.
 
Cheers guys.

Yea true I guess, perhaps it should have been tau as the differential.
 
This relates to the integral of exp[ iwt], between t and 0. This is then squared, so i was going to just integrate exp [ 2iwt].


The answer is 2(1 - coswt) / w ...i can't seem to get this at all. Any ideas?
 
Is it the integral that's squared, or just the integrand?
 
The integral
[tex]\int_0^t e^{-2i\tau}d\tau[/tex]
is
[tex]-\fra{1}{2i}e^{-2it}= \frac{i}{2}e^{-2it}[/tex]

NOT
[tex]\frac{2(1- cos(\omega t))}{\omega}[/tex]
or even
[tex]\frac{2(1- cos(2t))}{2}= 1- cos(2t)[/itex][/tex]
 

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