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Simple 3d trig problem

  1. Jun 12, 2010 #1
    1. The problem statement, all variables and given/known data
    [PLAIN]http://img708.imageshack.us/img708/1344/trig.jpg [Broken]
    The angle c is separated from a 2d plane by angle b (perpendicular to the 2d plane). Angle a is angle c projected onto the 2d plane. What is a in terms of b and c?


    2. Relevant equations



    3. The attempt at a solution
    I put the whole thing in a cuboid, used the lengths of the edges, and came to tan(a)=tan(b)tan(c). Can i just double check this with someone, because i dont trust my maths.:grumpy:
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jun 12, 2010 #2

    jack action

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    It doesn't work. When b = 0, no matter what c is, your equation gives a = 0, which doesn't make sense as a = c when b = 0.

    This seems more appropriate to me: tan a = tan c / cos b
     
  4. Jun 13, 2010 #3
    Yeah, it doesnt work, i probably should have checked some figures. I re-did it and i think i missed a 1. I got tan a = sqrt((tan b)^2 + 1) * tan c

    => tan a = sec b * tan c

    so yes, youre completely right, thanks.
     
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