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Reverse product rule?

  1. Nov 5, 2009 #1
    1. The problem statement, all variables and given/known data
    i'm sorry i know i've been bombarding physics forums with questions but i need help :p
    using reverse product rule [tex]\int uv'[/tex] = uv - [tex]\int vu'[/tex]
    and say i have a*b
    i noticed my teaher said that a=u and b=v not v' and he simly made that into a v' by deriving.
    is there a point to this if so what is the point and is this something he is likely to have done on purpose or by accident.


    2. Relevant equations
    ....and yes a*b = e^-y /y

    3. The attempt at a solution
    i attempted, but failed miserably.
     
  2. jcsd
  3. Nov 5, 2009 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    One of the things you are NOT doing that you should is including the "dx" or "dt" or whatever the variable of integration is. The correct statement of "integration by parts", which is, as you say, the "reverse product rule", is [itex]\int udv= uv- \int vdu[/itex].

    Now, I don't know what you mean by "say I have a*b". Do you mean you are trying to integrate [itex]\int a(x)b(x)dx[/itex]? In that case, you could try u= a, dv= bdx, then find du by differentiating and find v by integrating.
     
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