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Why cant i use substitution for this?

  1. Dec 6, 2011 #1
    Why doesn't substitution work to find 0∫2 sqrt(4-x^2). I kn ow you can find the integral in other ways. I am just curious why regular substitution won't work. Thank you in advance.
  2. jcsd
  3. Dec 6, 2011 #2
    If you make the substitution [itex] u=x^2 [/itex] then du = 2x dx. But you don't have a factor of 2x in the integrand. Or were you thinking of a different substitution? In any case, a trigonometric substitution would work better.
  4. Dec 6, 2011 #3


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    But substitution does work. Make the substitution x = 2cos(θ). Isn't that a "substitution"?
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