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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


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    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:
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