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Homework Help: Difficulty to find this integral

  1. May 7, 2012 #1
    1. The problem statement, all variables and given/known data
    Hi! I'm not being able to solve this integral: [tex]\int \sqrt{2ax}\; dx[/tex] We have started with integral yesterday and I don't know much yet.



    2. Relevant equations



    3. The attempt at a solution
    This is what I tried to solve the integral
    [tex]\int \sqrt{2ax}\; dx = \int u^{\frac{1}{2}}\; du = \frac{2}{3}{}u^{\frac{3}{2}}=\frac{2}{3}\sqrt[3]{(2ax)^2}[/tex]
     
  2. jcsd
  3. May 7, 2012 #2

    DryRun

    User Avatar
    Gold Member

    Assuming that a is a real constant,
    [tex]\int \sqrt{2ax}\; dx = \int \sqrt{2a}\sqrt x\; dx= \sqrt{2a} \int \sqrt x\; dx[/tex]
    Since [itex]\sqrt x[/itex] is the same as [itex]x^{\frac{1}{2}}[/itex], you can easily find its integral, and then multiply by [itex]\sqrt {2a}[/itex] to get the final answer.
     
  4. May 7, 2012 #3

    Mark44

    Staff: Mentor

    When you use a substitution, as you obviously did above, you need to write down what the substitution is. IOW, you should have u = <...> somewhere close by.

    Also, u3/2 = ##\sqrt{u^3}##, not ##\sqrt[3]{u^2}##, which is what you had.
     
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