25. 如图,在ΔABC\Delta ABCΔABC中,\angBAC=π3\ang BAC=\frac{\pi }{3}\angBAC=3π,AD→=2DB→\overrightarrow{AD}=2\overrightarrow{DB}AD=2DB,PPP为CDCDCD上一点,且满足AP→=mAC→+12AB→\overrightarrow{AP}=m\overrightarrow{AC}+\frac{1}{2}\overrightarrow{AB}AP=mAC+21AB,若AC=3AC=3AC=3,AB=4AB=4AB=4,则AP→⋅CD→\overrightarrow{AP}\cdot \overrightarrow{CD}AP⋅CD的值为 .