Khẳng định nào sau đây đúng? A. a .b =0⟺[(a ⃗=0 b =0 )

* Hướng dẫn giải

Ta có: $\overrightarrow{a}.\overrightarrow{b}=\left|\overrightarrow{a}\right|.\left|\overrightarrow{b}\right|.c\text{os }(\overrightarrow{a};\overrightarrow{b})$

Để $\overrightarrow{a}.\overrightarrow{b}=0\iff \left[\text{}\begin{array}{c}\left|\overrightarrow{a}\right|=0\\ \begin{array}{l}\left|\overrightarrow{b}\right|=0\\ c\text{os }(\overrightarrow{a};\overrightarrow{b})=0\end{array}\end{array}\right.\iff \left[\text{}\begin{array}{c}\overrightarrow{a}=\overrightarrow{0}\\ \begin{array}{l}\overrightarrow{b}=\overrightarrow{0}\\ \overrightarrow{a}\perp \overrightarrow{b}\end{array}\end{array}\right.$

Chọn D