An Integral With A Square Root In The Denominator

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SUMMARY

The discussion focuses on integrating the expression \(\int \frac{d \varphi}{\sqrt{1 + \frac{a^2 b^2 \sin^2 \alpha}{(a \sin \varphi + b \sin (\alpha - \varphi))^2}}}\). Participants suggest that while numerical methods may be simpler, a closed-form solution is preferred. Key strategies include rewriting the expression using negative exponents and employing techniques such as partial fractions and integration by parts. Additionally, it is noted that the terms within the square root can be simplified as perfect squares, leading to a transformation involving constants c and β.

PREREQUISITES
  • Understanding of integral calculus and techniques such as integration by parts.
  • Familiarity with trigonometric identities and transformations.
  • Knowledge of partial fraction decomposition.
  • Experience with numerical integration methods for comparison.
NEXT STEPS
  • Research techniques for integrating expressions with square roots in the denominator.
  • Study the method of integration by parts in greater detail.
  • Explore partial fraction decomposition for complex rational functions.
  • Learn about trigonometric substitutions and their applications in integration.
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Mathematicians, physics students, and anyone involved in advanced calculus or integral equations seeking to deepen their understanding of integration techniques and trigonometric transformations.

Radek Vavra
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How would you integrate it?

[itex]\int \frac{d \varphi}{\sqrt{1 + \frac{a^2 b^2 \sin^2 \alpha}{(a \sin \varphi + b \sin (\alpha - \varphi))^2}}}[/itex]

I know that solving it numerically would probably be easier, but I would prefer a closed form solution in this case.
 
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Try putting it as ^-.5 and also remember that a, b and sin^2(alpha) are all constants with respect to d(phi).
With that in mind try using partial fractions and/or By parts. Tell if You solve it!

Also pay attention to the fact that every term in the square root is a perfect square!
 
It is a little work, but as a first step: asinφ + bsin(α-φ) = csin(φ+β) where c and β are constants depending on a,b, and α.
 

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