# Thread: Find a*b

1. ## Find a*b

find $a*b$ if
$|a| = 4$, $|b|=8$, and the angle between $a$ and $b$ is [pi/-9] radians.

$a*b=$

2. $\cos \left( \phi \right) = \frac{{a \cdot b}}{{\left\| a \right\|\left\| b \right\|}}
$