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Homework Help: Simple Derivative question from a Calc beginner

  1. Oct 22, 2011 #1
    Hi I'm new in the forum, so if I'm doing anything wrong or made a really silly mistake don't laugh ^^

    So we started to learn about differentiating equations not long ago and I'm currently stuck at one question:

    y = e^αx sin βx

    My attempt on deriving it:


    the web program said it was wrong, please correct me :D
  2. jcsd
  3. Oct 22, 2011 #2


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    Aw, c'mon, we don't have much else to laugh at.

    Ah, blast! Your answer is correct!

    I really hate "web" assignments. Often something is marked wrong just because it is not written in the "right" form.

    Try entering it as [itex]ae^{ax}sin(\beta x)+ \beta e^{ax}cos(\beta x)[/itex] or [itex]e^{ax}(a sin(\beta x)+ \beta cos(\beta x))[/itex].
  4. Oct 22, 2011 #3
    sigh i tried a couple of variations but I ended up being locked up since I reached the maximum amount of trials. Thanks for the confirmation anyway ^^
  5. Oct 22, 2011 #4


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    Bring up the matter of your correct answer being rejected by the Web-system with your instructor. I've found that the more mathematically advanced the course is, the greater the likelihood that the program will call correct entries "wrong". (For instance, in WebAssign, you must say "(sin x)2", NEVER "sin2 x" !!!)

    I offered students the option of working with WebAssign in my calculus course a while back: they found the way of entering calculus expressions so cumbersome, and I had to check rejected answers so many times, that I'd never touch the accursed system for a course beyond algebra again...
  6. Oct 22, 2011 #5


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    You probably should make sure the parentheses are adequate. Also, you had an alpha when you gave us y = e^αx sin βx, then used the letter, a, in your derivative expression.

    I would enter: y'=(α)(e^(αx))(sin(βx))+(e(^αx))(cos(βx))(β)
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