2.(2023•西安模拟)在ΔABC\Delta ABCΔABC中,设AC→=a→\overrightarrow{AC}=\overrightarrow{a}AC=a,AB→=b→\overrightarrow{AB}=\overrightarrow{b}AB=b,GGG为ΔABC\Delta ABCΔABC的重心,则用向量a→\overrightarrow{a}a和b→\overrightarrow{b}b为基底表示向量GC→=(\overrightarrow{GC}=(GC=( )))