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Parameters for polar conics

  1. Nov 14, 2013 #1
    1. The problem statement, all variables and given/known data

    Hi wondering what the directrix is for this

    2. Relevant equations

    r = (20)/ (2+sin(theta))

    3. The attempt at a solution

    I factored denominator so it read 2(1+ (1/2)sin(theta)) ...So I said e times d = (2/20) and I got d = (1/5) because e is (1/2). Doesn't make sense though seems to small because that lies inside of the thing when I graph it.
     
  2. jcsd
  3. Nov 14, 2013 #2

    Simon Bridge

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    This bit you did OK - try working on the whole fraction though.
    $$r=\frac{20}{2+\sin\theta} = \frac{10}{1+\frac{1}{2}\sin\theta}=\frac{ed}{1+e\sin\theta}$$

    So ##e=\frac{1}{2}## right? And ##ed=\cdots##?
     
  4. Nov 15, 2013 #3
    d = 20? ed = 10 = (1/2) = 10
     
  5. Nov 15, 2013 #4

    Simon Bridge

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    Um... that is just nonsense. eg. 10 ≠ (1/2)

    You have to use reasonable grammar when you write sentences in any language.
    Math is also a language - therefore you should take some trouble to make sure the math/number sentences you write down actually mean something.

    Want to try again?
     
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