11.如图,点PPP,QQQ是线段的三等分点,以AP→,AQ→\overrightarrow{AP},\overrightarrow{AQ}AP,AQ为基底表示AB→=\overrightarrow{AB}=AB=[ ]{.underline}2AP→−AQ→2\overrightarrow{AP}-\overrightarrow{AQ}2AP−AQ[ ]{.underline}.