<Dd> e ^ i ⋅ (e ^ j × e ^ k) = ε i j k (\ displaystyle \ mathbf (\ hat (e)) _ (i) \ cdot (\ mathbf (\ hat (e)) _ (j) \ times \ mathbf (\ hat (e)) _ (k)) = \ varepsilon _ (ijk)) </Dd> <P> where δ is the Kronecker delta (which is one for i = j and zero else) and ε i j k (\ displaystyle \ varepsilon _ (ijk)) is the Levi - Civita symbol (which is one for permutations ordered as ijk and minus one for permutations ordered as kji). </P>

If a+b is a unit vector along x axis