1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: 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

    User Avatar
    Science Advisor
    Gold Member

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook