Elliptic Integral Homework: Calculate \int_{0}^{\pi/2}\frac{dx}{\sqrt{\sin{x}}}

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SUMMARY

The integral \(\int_{0}^{\pi/2}\frac{dx}{\sqrt{\sin{x}}}\) can be transformed into an elliptical form by substituting \( \sin(x) = \cos(\theta) \) and \( \theta = 2\phi \). This leads to the expression \(-2\int_{0}^{\pi/4}\frac{d\phi}{\sqrt{\cos{2\phi}}}\). Applying the double angle formula for cosine, the integral simplifies to \(2\int_{0}^{\pi/4}\frac{d\phi}{\sqrt{1-2(\sin\phi)^{2}}}\), which is equivalent to \(2F(\sqrt{2},\pi/4)\). However, Mathematica computes the result as \(\sqrt{2}K(1/2)\).

PREREQUISITES
  • Understanding of elliptic integrals, specifically the complete elliptic integral of the first kind.
  • Familiarity with trigonometric identities, particularly the double angle formula for cosine.
  • Proficiency in variable substitution techniques in calculus.
  • Basic knowledge of symbolic computation tools like Mathematica.
NEXT STEPS
  • Study the properties and applications of complete elliptic integrals, focusing on \(K(k)\).
  • Learn about the derivation and use of trigonometric identities in calculus.
  • Explore advanced integration techniques, including variable substitution and transformation methods.
  • Familiarize yourself with using Mathematica for symbolic integration and verification of results.
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Students and educators in mathematics, particularly those studying calculus and elliptic integrals, as well as researchers needing to compute complex integrals using symbolic computation tools.

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Homework Statement



The problem is to calculate integral \int_{0}^{\pi/2}\frac{dx}{\sqrt{\sin{x}}} by transforming it into elliptical form (complete elliptical integral of first kind).
 
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First substitute a new variable theta with sin(x) = cos(theta). Then substitute a new variable phi with theta = 2 phi. Then you should have:

sed to generate this LaTeX image:


<br /> -2\int_{0}^{\pi/4}\frac{d\phi}{\sqrt{\cos{ 2\phi}}}<br />

Now use the double angle formula for cosine given by cos(2a) = 1 - 2 Sin(a)^2 and you should be home free.
 
Thanks. I get it to the form 2\int_{0}^{\pi/4}\frac{d\phi}{\sqrt{1-2(sin\phi)^{2}}}, which in my opinion equals 2F(\sqrt{2},\pi/4), but according to Mathematica, the answer is \sqrt{2}K(1/2).
 

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