Trong mặt phẳng \(Oxy\) cho \(\overrightarrow a = \left( {1;3} \right),\;\overrightarrow b  = \left( { - 2;1} \right)\). Tích vô hướng của 2 vectơ \(\overrightarrow a .\overrightarrow b \) là:

\(16\).

\(26\).

\(36\).

\( - 16\).

\(\overrightarrow a .\overrightarrow b  = \left| {\overrightarrow a } \right|.\left| {\overrightarrow b } \right|\).

\(\overrightarrow a .\overrightarrow b  = 0\).

\(\overrightarrow a .\overrightarrow b  =  - 1\).

\(\overrightarrow a .\overrightarrow b =  - \left| {\overrightarrow a } \right|.\left| {\overrightarrow b } \right|\).

\(3\).

\(4\).

\(1\).

\(2\).

${45^{\rm{o}}}$.

${\rm{6}}{{\rm{0}}^{\rm{o}}}$.

${\rm{3}}{{\rm{0}}^{\rm{o}}}$.

${\rm{13}}{{\rm{5}}^{\rm{o}}}$.

\(\overrightarrow {OA} .\overrightarrow {OB}  = 0\).

\(\overrightarrow {OA} .\overrightarrow {OC}  = \dfrac{1}{2}\overrightarrow {OA} .\overrightarrow {AC} \).

\(\overrightarrow {AB} .\overrightarrow {AC}  = \overrightarrow {AB} .\overrightarrow {CD} \).

\(\overrightarrow {AB} .\overrightarrow {AC}  = \overrightarrow {AC} .\overrightarrow {AD} \).

\(\cos B = \dfrac{1}{{\sqrt 3 }}\).

\(\sin C = \dfrac{{\sqrt 3 }}{2}\).

\(\cos C = \dfrac{1}{2}\).

\(\sin B = \dfrac{1}{2}\)