Question
If $ \vec{a} $, $ \vec{b} $, and $ \vec{c} $ are unit vectors such that $ \vec{a} + \vec{b} + \vec{c} = \vec{0} $, then the angle between $ \vec{a} $ and $ \vec{b} $ is ........
If $ \vec{a} $, $ \vec{b} $, and $ \vec{c} $ are unit vectors such that $ \vec{a} + \vec{b} + \vec{c} = \vec{0} $, then the angle between $ \vec{a} $ and $ \vec{b} $ is ........