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Homework Help: Is wolfram wrong?

  1. Sep 26, 2011 #1
    1. The problem statement, all variables and given/known data

    Wolfram says the derivative of (sin x)^2 is sin2x. Shouldn't it be 2(sin x)(cos x)?
  2. jcsd
  3. Sep 26, 2011 #2


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    Staff: Mentor

    Are these results different?
  4. Sep 26, 2011 #3

    Why on earth is that? Which of the umpteen trigonometric identities?
  5. Sep 26, 2011 #4
    They are the same. This is the double angle formula for sine.
  6. Sep 26, 2011 #5


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    Staff Emeritus
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    sin(2x) = 2 sin(x) cos(x)

    You can get this from sin(2x) = sin(x + x)
    = sin(x) cos(x) + cos(x) sin(x)

    = 2 sin(x) cos(x)​
  7. Sep 26, 2011 #6
    Trigonometry really pisses me off sometimes.
  8. Sep 26, 2011 #7


    Staff: Mentor

    If you're working toward a degree in physics and/or math, you had better get a solid handle on trig.
  9. Sep 26, 2011 #8
    I like using it for things like vectors, I just don't like the identities. They feel "synthetic."
  10. Sep 26, 2011 #9


    Staff: Mentor


    The identities are there to help you out. In your other current post, you put in a lot more work than was necessary, by not using a fairly simple identity: cos(2x) = cos2(x) - sin2(x).
  11. Sep 26, 2011 #10
    these identities can be derived using Eulers formula.
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