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Homework Help: Simple Derivative Problem

  1. Aug 13, 2012 #1
    Find the derivative of (4995)/(1+.12cosθ), when θ = 120°

    My attempt:

    d/dx [4995/(1+.12cosθ) = (4995)(-1)(1+.12cosθ)-2(.12)(-sinθ)

    Letting θ = 120°...

    = (4995)(-1)(1+.12(-1/2))-2(.12)(-[itex]\sqrt{3}[/itex]/2)

    My calculator says that is about 587.478

    But it's supposed to be about 10.253

    I just started calculus, so I'm probably making some really basic mistake.
  2. jcsd
  3. Aug 13, 2012 #2


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    Science Advisor

    Results are usually done in radians instead of degrees. Have you tried doing your

    computation in radians?
  4. Aug 13, 2012 #3


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    Science Advisor
    Homework Helper
    Gold Member

    To add to what Bacle2 has said, your standard formulas for the derivatives are correct only when the angles are given in radians.
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