Regarding signed dihedral angle doubt

[sureshjrf]

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...

 

[tiny-tim]

Welcome to PF!

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!

Cos doesn't care about the sign …

cos(x) = cos(-x).
​

So cos(135.9) = cos(-135.9).