Question
If $\vec{a}$ and $\vec{b}$ are two unit vectors such that $|\vec{a} + \vec{b}| = 2\sqrt{3}$ and $|\vec{a} - \vec{b}| = 6$, then the angle between $\vec{a}$ and $\vec{b}$ is
If $\vec{a}$ and $\vec{b}$ are two unit vectors such that $|\vec{a} + \vec{b}| = 2\sqrt{3}$ and $|\vec{a} - \vec{b}| = 6$, then the angle between $\vec{a}$ and $\vec{b}$ is