3.在ΔABC\Delta ABCΔABC中,已知DDD是ABABAB边上的中点,GGG是CDCDCD的中点,若AG→=λAB→+μAC→\overrightarrow{AG}=\lambda \overrightarrow{AB}+\mu \overrightarrow{AC}AG=λAB+μAC,则实数λ+μ=(\lambda +\mu =(λ+μ=( )))