If $ \vec{a} $ and $ \vec{b} $ are unit vectors such that $ \vec{a} \cdot \vec{b} = \cos \theta $, then the value of $ |\vec{a} + \vec{b}| $ is:

Question

$2 \sin \left(\dfrac{\theta}{2}\right)$

$2 \sin \theta$

$2 \cos \left(\dfrac{\theta}{2}\right)$

$2 \cos \theta$

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