1D
2C
3C
4. \(\overrightarrow{AB}.\overrightarrow{AC}=AB.AC.cos60^0=\dfrac{a^2}{2}\)
5. Do tam giác vuông tại A \(\Rightarrow AB\perp AC\Rightarrow\overrightarrow{AB}.\overrightarrow{AC}=0\)
6. \(\overrightarrow{AB}.\overrightarrow{AC}=AB.AC.cos60^0=2a^2\)
7. \(\overrightarrow{AB}.\overrightarrow{AC}=AB.AC.cos45^0=\dfrac{a^2\sqrt{2}}{2}\)