Mathematics

Problem

Let

\vec{a}, \vec{b}

and

\vec{c}

be three unit vectors such that

\vec{a} \times (\vec{b} \times \vec{c}) = \frac{\sqrt{3}}{2}(\vec{b} + \vec{c})

. If

\vec{b}

is not parallel to

\vec{c}

, then the angle between

\vec{a}

and

\vec{b}

is: a.

\frac{3\pi}{4}

\frac{\pi}{2}

\frac{2\pi}{3}

\frac{5\pi}{6}