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Derivative of a trig. function

  1. Jul 14, 2012 #1
    1. Find the derivative of the function using the power rule or product rule



    2. sinθ/2 + c/θ



    3. I tried to do plus or minus the √1-cosθ/2
     
  2. jcsd
  3. Jul 14, 2012 #2

    eumyang

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    Your question is ambiguous. Please use parentheses. It looks like that want to find the derivative of
    [tex]\frac{\sin \theta}{2} + \frac{c}{\theta}[/tex]
     
  4. Jul 14, 2012 #3
    Yes, that's it
     
  5. Jul 14, 2012 #4
    There is no need to plus or minus the √1-cosθ/2, simply find the derivative of sin θ and 1/θ w.r.t θ (I suppose that's what you are asked.) And what about c? How is it defined in the question?
     
  6. Jul 14, 2012 #5
    Here's what I have (cosθ/2) + (c/θ). c is a variable.
     
    Last edited: Jul 14, 2012
  7. Jul 14, 2012 #6
    The c probably stands for some constant.
     
  8. Jul 14, 2012 #7
    ok, thanks.
     
  9. Jul 14, 2012 #8

    eumyang

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    If c is a constant, and the above is your solution attempt, then you have to do something with the 2nd term (ie. the derivative of c/θ isn't c/θ).
     
  10. Jul 14, 2012 #9
    The solution would be (cosθ/2).
     
  11. Jul 14, 2012 #10
    No, how do you get this? What's the derivative of 1/θ?
     
  12. Jul 14, 2012 #11
    The derivative of a constant is 0.
     
  13. Jul 14, 2012 #12

    eumyang

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    Sorry, that's wrong. If the original problem was this:
    [tex]\frac{\sin \theta}{2} + c[/tex]
    (with c as a constant), then your answer would be right. But the 2nd term has a θ in the denominator. What do we do?
     
  14. Jul 14, 2012 #13
    It would be (cosθ/2 - c/θ^2)
     
  15. Jul 14, 2012 #14
    Looks good.
     
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