Which of the following relations is true for two unit vector $\widehat A$ and $\widehat B$ making an angle $\theta$ to each other?

Question

$|\widehat A + \widehat B| = |\widehat A - \widehat B|\tan {\theta \over 2}$

$|\widehat A - \widehat B| = |\widehat A + \widehat B|\tan {\theta \over 2}$

$|\widehat A + \widehat B| = |\widehat A - \widehat B|cos{\theta \over 2}$

$|\widehat A - \widehat B| = |\widehat A + \widehat B|\cos {\theta \over 2}$

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