Complex Integration: Solving $\int_0^1\frac{2t+i}{t^2+it^2+1}dt$

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Discussion Overview

The discussion revolves around the evaluation of the integral $\int_0^1\frac{2t+i}{t^2+it^2+1}dt$. Participants explore potential methods for solving the integral, including considerations of possible typos in the expression and the relationship between the numerator and denominator.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant presents an expression for the integral and attempts to simplify it by multiplying through by the conjugate, but finds it unfruitful.
  • Another participant suggests that there may be a typo in the denominator, proposing it should be $\int_0^1\frac{2t+i}{t^2+it+1}dt$ instead.
  • This same participant notes that if the proposed correction is valid, the numerator is the derivative of the denominator, leading to a straightforward evaluation of the integral as $\left[\ln(t^2+it+1)\right]_0^1 = \ln(2+i) = \sqrt5 + i\tan^{-1}\frac12$.
  • A subsequent post questions the expression for the logarithm, suggesting it should be $\ln\sqrt{5} + i\tan^{-1}\frac{1}{2}$, to which another participant agrees.

Areas of Agreement / Disagreement

There is uncertainty regarding the correctness of the denominator in the integral, with multiple participants suggesting a possible typo. While some participants agree on the evaluation method if the correction is accepted, there is no consensus on the original expression's validity.

Contextual Notes

The discussion includes potential limitations related to the assumptions about the denominator's form and the implications of these assumptions on the evaluation of the integral.

Dustinsfl
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$\displaystyle\int_0^1\frac{2t+i}{t^2+it^2+1}dt = \int_0^1\frac{2t^3+3t+i-it^2}{t^4+3t^2+1}dt =\int_0^1\frac{2t^3+3t}{t^4+3t^2+1}dt+i\int_0^1 \frac{1-t^2}{t^4+3t^2+1}dt$

I tried multiplying through by the conjugate but that didn't seem fruitful and left me with the above expression. Is there a better way to tackle this problem?

Typo I mixed up two parts
 
Last edited:
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dwsmith said:
$\displaystyle\int_0^1\frac{2t+i}{t^2+it^2+1}dt$
For a start, it looks as though there is a typo in the denominator. Shouldn't it be $\int_0^1\frac{2t+i}{t^2+it+1}dt$ ?

If so, the numerator is the derivative of the denominator, and the integral is
$\left[\ln(t^2+it+1)\right]_0^1 = \ln(2+i) = \sqrt5 + i\tan^{-1}\frac12$.
 
Last edited:
Opalg said:
For a start, it looks as though there is a typo in the denominator. Shouldn't it be $\int_0^1\frac{2t+i}{t^2+it+1}dt$ ?

If so, the numerator is the derivative of the denominator, and the integral is
$\left[\ln(t^2+it+1)\right]_0^1 = \ln(2+i) = \sqrt5 + i\tan^{-1}\frac12$.

Shouldn't that be $\ln\sqrt{5} + i\tan^{-1}\frac{1}{2}$?
 
dwsmith said:
Shouldn't that be $\ln\sqrt{5} + i\tan^{-1}\frac{1}{2}$?
Yes! (Doh)
 

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