Regarding signed dihedral angle doubt

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    Angle Dihedral Doubt
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SUMMARY

The discussion centers on calculating signed dihedral angles, specifically the Phi Psi angles, in bioinformatics. The user calculated a dihedral angle using the formula cos(theta) = (A.B/|A||B|) and obtained a value of 135.9 degrees. However, the user seeks clarification on how to derive the signed value of -135.9 degrees. The response highlights that the cosine function does not differentiate between positive and negative angles, as cos(135.9) equals cos(-135.9).

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sureshjrf
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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...
cos(theta)=(A.B/|A||B|)

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

my program value..
theta=cos inverse of (-0.717563607965311)
theta=135.9,

But i need the result as -135.9

tanks in advance...
 
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Welcome to PF!

sureshjrf said:
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...
cos(theta)=(A.B/|A||B|)
…
my program value..
theta=cos inverse of (-0.717563607965311)
theta=135.9,

But i need the result as -135.9

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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