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Calculation of length inside a circle

  1. Nov 2, 2008 #1
    1. The problem statement, all variables and given/known data
    [​IMG]

    I want to find the length in red
    radius is 10, angle is 30°
    Is it possible?

    2. Relevant equations
    30° = pi/6
    I can find the arc using arc length = r theta
    = 10 * pi/6
    = 5/3pi



    3. The attempt at a solution
    But now where. What can i use to find the red line?

    Thanks
     
    Last edited: Nov 2, 2008
  2. jcsd
  3. Nov 2, 2008 #2

    rock.freak667

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    Is the red line perpendicular to that horizontal line that makes 30 degrees?
     
  4. Nov 2, 2008 #3
    yep. is it possible to find the red line?
     
  5. Nov 2, 2008 #4

    symbolipoint

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    You have half of an equilateral triangle.
     
  6. Nov 2, 2008 #5

    rock.freak667

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    If it is perpendicular, then just consider what cos30 is and what sin30 is.
     
  7. Nov 2, 2008 #6
    this is for a project not a homework question so im not really bothered about being walked through. can you give it to me in all one go please? I know you walk people through homeworks, but I need this quite quickly :)

    half an equilateral triangle because of a circle rule?
    what next?
    so can you DEFINAtLY calculate the the red line?

    Thank you :)
     
  8. Nov 2, 2008 #7
    Wow, it's so simple, I was looking for much more complicated stuff. I know the hypotenuse and the angle therefore i can calculate the length of the opposite side using trig
     
  9. Nov 2, 2008 #8

    symbolipoint

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    The situation is simpler than that. You do not need any Trigonometry. My hint was, "you have half of an equilateral triangle." Half of an equilateral triangle is a 30-60-90 triangle; put the two halves together and you have the whole equilateral triangle. Your red segment is half of a side of the equilateral triangle. Each side of the equilateral triangle formable from your diagram is 10 units. Your red segment by itself in your diagram is 5 units.
     
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