Question

Answer 1

Lời giải:

a.

$\angle (\overrightarrow{AB}, \overrightarrow{AD})=\angle BAD =90^0$
$\angle (\overrightarrow{AB}, \overrightarrow{AC})=\angle BAC=45^0$

Dựng vector $\overrightarrow{AF}$ sao cho $\overrightarrow{AF}=\overrightarrow{CA}$

Ta có:

$\angle (\overrightarrow{AB}, \overrightarrow{CA})=\angle (\overrightarrow{AB}, \overrightarrow{AF})=\widehat{FAB}=180^0-45^0=135^0$

Answer 2

b,

Theo công thức cos 2 hai vector thì:

$\overrightarrow{AB}.\overrightarrow{AD}=\cos (\overrightarrow{AB}, \overrightarrow{AD}).|\overrightarrow{AB}|.|\overrightarrow{AD}|$

$=\cos 90^0.2.2=0$