$[-/2$ Points$]$

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SCALCET$912\mathrm{.}3\mathrm{.}017.$

Find the angle between the vectors. $($First find an exact expression and then approximale to the neurest degree.$)$

$a=($:$1,-4,1$:$),b=($:$0,8,-1$:$)$:

exact

approximate $$

Need Holn? $$