Which of the following relations is true for two unit vector \( \vec{A} \) and \( \vec{B} \) making an angle \( \theta \) to each other?
\( |\vec{A} + \vec{B}| = |\vec{A} - \vec{B}| \tan \frac{\theta}{2} \)
\( |\vec{A} - \vec{B}| = |\vec{A} + \vec{B}| \tan \frac{\theta}{2} \)
\( |\vec{A} + \vec{B}| = |\vec{A} - \vec{B}| \cos \frac{\theta}{2} \)
\( |\vec{A} - \vec{B}| = |\vec{A} + \vec{B}| \cos \frac{\theta}{2} \)