$5\mathrm{.}25$ Points$]$

$$ SCALC$714\mathrm{.}6\mathrm{.}016.$

Find the directional derivative of the function at the given point in the direction of the vector $v.$

$f(x,y,z)=\sqrt[\phantom{2}]{xyz},(3,2,6),v=(-1,-2,2)$

$D_{u}f(3,2,6)=$

$$