Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Regarding signed dihedral angle doubt

  1. Dec 7, 2008 #1
    Hi to all..
    I am doing Phd in bioinformatics, having little knowledge abt maths..
    I have calculated Phi Psi angles(dihedral angle)between two planes...
    But the thing is i didnt get proper sign for my result(may be + or -).
    I used following formulae for calculate the dihedral angle between two planes...

    any one help me how can i get the signed values for my result..

    my program value..
    theta=cos inverse of (-0.717563607965311)

    But i need the result as -135.9

    tanks in advance...
  2. jcsd
  3. Dec 8, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi sureshjrf! Welcome to PF! :smile:

    Cos doesn't care :rolleyes: about the sign …

    cos(x) = cos(-x).

    So cos(135.9) = cos(-135.9). :wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook