find $\displaystyle a*b$ if $\displaystyle |a| = 4$, $\displaystyle |b|=8$, and the angle between $\displaystyle a$ and $\displaystyle b$ is [pi/-9] radians. $\displaystyle a*b=$
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$\displaystyle \cos \left( \phi \right) = \frac{{a \cdot b}}{{\left\| a \right\|\left\| b \right\|}} $