Ok, so i have Vectors A + B + C = 0
From this, am i right in thinking that it forms an equilateral triangle? Or is that incorrect?
I need to use the above to find the answer to a.b + b.c + c.a
Before, you left out a most important word: UNIT.
Because they are units, recall that $\displaystyle \left\| A \right\|=1$
$\displaystyle \begin{gathered}
\left( {A + B + C} \right) \cdot \left( {A + B + C} \right) = 0 \hfill \\
\left\| A \right\|^2 + \left\| B \right\|^2 + \left\| C \right\|^2 + 2A \cdot B + 2A \cdot C + 2C \cdot B = 0 \hfill \\
\end{gathered} $