If \(\vec{a}\), \(\vec{b}\), \(\vec{c}\) are unit coplanar vectors, then scalar triple product [2\(\vec{a}\) - \(\vec{b}\)  2\(\vec{b}\) - \(\vec{c}\)  2\(\vec{c}\) - \(\vec{a}\)] is equal to : 

0

Since \(\vec{a}\), \(\vec{b}\), \(\vec{c}\) are unit coplanar vector ⇒ [\(\vec{a}\)\(\vec{b}\)\(\vec{c}\)] = 0

So 2\(\vec{a}\) - \(\vec{b}\), 2\(\vec{b}\) - \(\vec{c}\), 2\(\vec{c}\) - \(\vec{a}\) are also coplanar vectors

Hence, [2\(\vec{a}\) - \(\vec{b}\)  2\(\vec{b}\) - \(\vec{c}\)  2\(\vec{c}\) - \(\vec{a}\)] = 0