Math teachers, can you help me out with this calculus question?

Discussion in 'Secondary Education' started by Peachyness, Dec 15, 2009.

  1. Peachyness

    Peachyness Virtuoso

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    [​IMG]
     
  2.  
  3. Peachyness

    Peachyness Virtuoso

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    okay, that didn't come out well.

    So, it's

    x(x+3)^(1/2)dx

    I know you need to do the u substitution.

    so, u=x+3, but du=dx, right? So, what do I do with the x in front of the (x+3)??
     
  4. Aliceacc

    Aliceacc Multitudinous

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    It'a a little hard to read; are you integratng (x+3) to the one half??

    If so, isn't it (x+3) to the 3/2, times 2/3?? I think that, as long as it's one x to the first, it's pretty straight forward.

    That said, I haven't touched calc since 2000, so check my work!
     
  5. Aliceacc

    Aliceacc Multitudinous

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    Sorry Peachy, I misread the question and now have a feverish child in my lap as I type; I'm of no help to you tonight!
     
  6. mmswm

    mmswm Moderator

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    If u=x + 3, then x = u-3, right? You can back substitute and get

    (u -3)u^1/2, then multiply though to get u^3/2 -3u^1/2, which you can easily integrate with the power rule.
     
  7. Peachyness

    Peachyness Virtuoso

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    Let's try this again:
    [​IMG][​IMG]
     
  8. mmswm

    mmswm Moderator

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    Didn't work. :D Did you understand what I typed. Math characters are so hard to type on this forum..
     
  9. Peachyness

    Peachyness Virtuoso

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    you must have posted when I was trying to get this to work. Someone posted a thread on how to do this but, I can't get it to work.... oh well. OKay, I'm going to work out the problem based on what you wrote and see if I can "get it". Thanks!
     
  10. Peachyness

    Peachyness Virtuoso

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    OOOOOOOOOOOOOOOOOOOOOOOOHHHHHHHH, I got it! Thanks!!!
     
  11. mmswm

    mmswm Moderator

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    You're welcome. Don't forget that the solution to most of these 'tricky" problems is usually some sort of simple manipulation. Students get so caught up in the problem being "hard" that they forget to look at the simple things.
     
  12. Peachyness

    Peachyness Virtuoso

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    Yeah, no kidding! Man, that really was so simple, and yet I spent so long staring at that problem.... tsk tsk... thanks! :D
     
  13. Aliceacc

    Aliceacc Multitudinous

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    Sorry I was of no help; I had to strip a bed and get Julia all settled.
     
  14. Peachyness

    Peachyness Virtuoso

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    Oh, Alice, that is all right! I know you're a super busy mom. :)
     
  15. TeacherGroupie

    TeacherGroupie Moderator

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    Peachy, if you haven't got one, you might want copies of either of these:

    Calculus for Cats, by Amdahl and Loats
    Misteaks, and How to Find Them Before the Teacher Does, 3d ed., by Barry Cipra
     
  16. Teaching_101

    Teaching_101 Companion

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    :eek:

    Are you sure you just spoke English?
     
  17. HMM

    HMM Cohort

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    [​IMG]

    Code:
    http://latex.codecogs.com/gif.latex?\int{x(x+3)^{1/2}}dx
     
  18. HMM

    HMM Cohort

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    You can also use integration by parts (if you know how to do that)...though what mmswm did will work just fine.
     
  19. mmswm

    mmswm Moderator

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    I thought about using parts, but it was easier to substitute...at least is was easier to explain on this forum that way. I find that there's rarely only one way to attack a problem. The other reason I went with the way I did is because I wasn't sure what course the OP is taking. I know we didnt' introduce by parts unti Calc2, though there was some simple integration at the end of calc1.
     
  20. HMM

    HMM Cohort

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    I'm betting that the OP has not done integration by parts (based on the type of question asked), but I thought I'd throw out the idea anyway.
     
  21. HMM

    HMM Cohort

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    I thought about going through a power series solution, but then figured that might be a little overkill :p
     

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