1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Trig question - segment angle

  1. Nov 22, 2006 #1
    Hi,
    I have a segment of a circle, and know the following quantities.
    I need to find cos(BETA), and I know that it's supposed to be = (L^2 - 4h^2)/(L^2 + 4h^2), and I've been trying this for hours.. I suppose it has something to do with the triangle - as you can find the 3rd side (=radius-h), but I just can't get it.. Can somebody please help me out?

    [​IMG]
     
  2. jcsd
  3. Nov 22, 2006 #2
    You could use the Pythagorean Theorem to find the 3rd side. But, there is too much information, so [tex]\cos\beta[/tex] can be expressed many ways.
     
  4. Nov 23, 2006 #3
    I just took the 3rd side to be R-h.
     
  5. Nov 23, 2006 #4

    Integral

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Could you show me how you came up with

    [tex] \frac {L^2 + 4h^2} {8h}[/tex] for the hypotenuse. Why not just call it what it is R?
     
  6. Nov 23, 2006 #5
    Because the 1st part of the question asked me to show that R = that. I got it by Pythagoras theorem...

    R^2 = (L/2)^2 + (R-h)^2 (pythag)
    R^2 = L^2/4 + R^2 - 2hR + h^2 (expand square terms)
    2hR = L^2/4 + h^2 (gather like terms)
    8hR = L^2 + 4h^2 (multiply through by 4)
    R = (L^2 + 4h^2)/8h (rearrange for R)


    The second part of the question is to find cos(BETA) where beta is the half angle, using the above result, and I'm totally stuck on that part.
     
  7. Nov 23, 2006 #6
    Solved

    Never mind guys - I got it eventually! :) Thanks for trying to help though! :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Trig question - segment angle
  1. Trig, angles etc (Replies: 8)

  2. Double Angle Trig (Replies: 5)

Loading...