Let a=8i4j+1k\displaystyle \vec{{a}}={8}\vec{{{i}}}-{4}\vec{{{j}}}+{1}\vec{{{k}}} and b=2i+6j9k\displaystyle \vec{{b}}={2}\vec{{{i}}}+{6}\vec{{{j}}}-{9}\vec{{{k}}}. Find ab\displaystyle \vec{{a}}\cdot\vec{{b}}