Deriving this "familiar arccosine form" of integral

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SUMMARY

The discussion centers on deriving the "familiar arccosine form" of an integral related to orbital dynamics, specifically the expression $$-\int \frac{1}{\sqrt{a+2 bx-hx^2}} \, dx=\frac{1}{\sqrt{h}}\arccos \left[\frac{b-hx}{\sqrt{a+b^2h}}\right]$$. The participants explore the geometric significance of the constants and variables in the context of an ellipse, suggesting that the method used in simpler cases may be generalizable. A reference to a Berkeley math resource is provided for further insight into the arccosine form, although it does not cover the more complex expression discussed.

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  • Understanding of integral calculus, specifically techniques involving arccosine functions.
  • Familiarity with the geometry of ellipses and their properties.
  • Knowledge of orbital dynamics and its mathematical representations.
  • Basic proficiency in manipulating algebraic expressions involving square roots and trigonometric functions.
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  • Research the geometric properties of ellipses and their applications in physics.
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Odious Suspect
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I posted a question about this yesterday, but realized I had made a stupid mistake in my derivation.
Orbital dynamics: "The familiar arc-cosine form"
That error has been corrected. I still have a deeper question. I believe this expression can be developed using the geometry of an ellipse in a way which adds insight into the original physics where it is being applied.

Some 30 odd years ago I saw something of this nature done in an introductory physics course.

Is anybody here familiar with such a development?

$$-\int \frac{1}{\sqrt{a+2 bx-hx^2}} \, dx=\frac{1}{\sqrt{h}}\arccos \left[\frac{b-hx}{\sqrt{a+b^2h}}\right]$$
 
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I am not sure what to do with your post, do you want to prove the above equation or what?
 
No. I can prove it. I want a geometric development. That is to say, I believe the constants and variables in the expression ##cos \theta = \frac{b-hx}{\sqrt{a+b^2h}}## have some geometric significance pertaining to an ellipse.
 
That only addresses the form I really am familiar with. Notice that the form I am asking about is more complicated.
 
Odious Suspect said:
That only addresses the form I really am familiar with. Notice that the form I am asking about is more complicated.

Yes, I know that you are asking about something more complicated.
Might it be the case that the method used in the simple case can be generalized? I don't know. I offered a possible starting point.
Sorry, if I didn't provide you with exactly what you seek.
 
Last edited:
Sorry about being so abrupt. I get grouchy when I can't figure something out.

I'm guessing this might be something to do with rotation of coordinates to eliminate the "cross product" term.

In some universe, the denominator in the cosine expression represents a radius.
 

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