Integrating Square Root of a Rational Function with Variable Substitution

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SUMMARY

The integration of the function $$\int \sqrt{\frac{r^{2}-x^{2}+x^{2}}{r^{2}-x^{2}}} dx$$ can be simplified using the substitution \( u = \frac{x}{r} \). This leads to a standard integral that can be solved using trigonometric substitution, specifically \( x = r \sin(t) \). The discussion confirms that other substitutions, such as \( u = r^2 - x^2 \) or \( u = x^2 \), do not yield the correct results.

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vee6
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How to integrate below?

$$\int \sqrt{\frac{r^{2}-x^{2}+x^{2}}{r^{2}-x^{2}}} dx$$

neither if u = r^2 - x^2 nor u = x^2 will get the result.
 
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Try u=x/r, and simplify, it should become a standard integral (solvable with formulas, or with a trigonometric substitution)
 
vee6 said:
How to integrate below?

$$\int \sqrt{\frac{r^{2}-x^{2}+x^{2}}{r^{2}-x^{2}}} dx$$

neither if u = r^2 - x^2 nor u = x^2 will get the result.
Is this really what you meant? Since -x^2+ x^2= 0 the is exactly the same as
|r|\int \frac{1}{\sqrt{r^2- x^2}}dx

The substitution x= sin(t) would be a stadard technique for this.
 

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