If , , and , then verify are NOT mutually perpendicular.

If $|\vec{a}| = 1$, $|\vec{b}| = 2$, $|\vec{c}| = 3$ and $\vec{a} + \vec{b} + \vec{c} = 0$, then verify $\vec{a}, \vec{b}, \vec{c}$ are NOT mutually perpendicular.