22.与a→=(1,2,−2)\overrightarrow{a}=(1,2,-2)a=(1,2,−2)同向的单位向量b→\overrightarrow{b}b是 ___(13(\frac{1}{3}(31[,]23\frac{2}{3}32[,]−23)-\frac{2}{3})−32)___.