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Homework Help: Is this trigonometric solution correct?

  1. Aug 25, 2013 #1
    1. The problem statement, all variables and given/known data

    Solve for y':

    4[(cos x)(cos y)(y') + (sin y)(-sin x)] = 0

    2. Relevant equations


    3. The attempt at a solution

    4[(cos x)(cos y)(y') + (sin y)(-sin x)] = 0

    4y' (cos x) (cos y) - 4 (sin x) (sin y) = 0

    4y' (cos x) (cos y) = 4 (sin x) (sin y)

    y' = [4 (sin x) (sin y)] / [4 (cos x) (cos y)]

    y' = (sin x sin y) / (cos x cos y)

    Thanks! I am really shaky at trigonometry, so the above worries me.
  2. jcsd
  3. Aug 25, 2013 #2


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    Homework Helper

    Yes that is correct. If you want to, you can simplify it even more using the fact that sinA/cosA = tanA.
  4. Aug 25, 2013 #3
    Thanks rock.freak667! See what I mean? I didn't even see that in the equation, although I do know that tan x = sin x/cos x.
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