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How to solve these integrals? sqrt(a^2 + x^2) & sqrt(2 + x^2)?

  1. Aug 17, 2010 #1
    How to solve these integrals, such as- sqrt(a^2 + x^2) & sqrt(2 + x^2)

    Please be as descriptive and simple as possible.

    Please use only sin and cos if possible We are not allowed a calculator in the exam and will have to find numerical values.
     
  2. jcsd
  3. Aug 17, 2010 #2

    disregardthat

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    For the first: try the substitution [tex]x = a \sinh(\theta) = a\frac{e^{\theta}-e^{-\theta}}{2}[/tex]
     
  4. Aug 18, 2010 #3

    HallsofIvy

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    Or use a trig substitution: [itex]x= a tan(\theta)[/itex]. Then [itex]a^2+ x^2= a^2+ a^2tan^2(\theta)[/itex][itex]= a^2(1+ tan^2(\theta))= a^2 sec^2(\theta)[/itex]. [itex]\sqrt{a^2+ x^2}= |a sec(x)|.

    And, of course, [itex]dx= a(tan(\theta))' d\theta= a sec^2(\theta)d\theta[/itex]

    I hope you recognize that the second problem, with [itex]\sqrt{2+ x^2}[/itex], is exactly the same as the first problem with [itex]a= \sqrt{2}[/itiex].
     
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