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Nth derivative

  1. Jul 26, 2015 #1
    i have solved the following one but not sure...anyone give me the solve..i want to be sure..

    nth derivative of {e^ax * Sin(ax+b)}
     
  2. jcsd
  3. Jul 27, 2015 #2

    andrewkirk

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    Show your solution and your working, as requested in the sub-forum guidelines, and I'm sure somebody will confirm it, or correct it if wrong.

    You need to use the product rule. Once you've differentiated several times you'll see a cyclic pattern that can be written down as a set of four cases.
     
  4. Jul 27, 2015 #3
    ok..here is my solution...somebody plz confirm me..

    b^n * e^ax * Sin {(n*pi/2)+(bx+c)} + n*a*b* e^ax * Sin {pi/2+(bx+c)} + a^n * e^ax * Sin (b+c)
     
  5. Jul 28, 2015 #4

    andrewkirk

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    Substitute n=1 into your formula and then compare to what you get when you differentiate once, ie ##\frac{d}{dx}\big(e^{ax}\sin(ax+b)\big)##.

    Do they look the same?

    Post the working by which you arrived at your conclusion and somebody can show where you went wrong. Did you try what I suggested in post 2?

    If you use latex to properly display your formulas you will also improve your chances of getting help. The latex tutorial is here.
     
  6. Jul 29, 2015 #5

    HallsofIvy

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    Your original function has "ax+ b" while your formula for the nth derivative has "bx+ c". Was one of those a misreading?
     
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