Mathematics

Problem

\vec{a}

and

\vec{b}

are the two vectors such that

|\vec{a}| = 3\sqrt{3}

|\vec{b}| = 4

and

|\vec{a} + \vec{b}| = \sqrt{7}

, then the angle between

\vec{a}

and

\vec{b}

is (a)

120^\circ

(b)

60^\circ

(d)

150^\circ

(c)

30^\circ