Cho các vectơ $\overrightarrow a ,\overrightarrow b \ne \overrightarrow 0$ . Phát biểu nào sau đây là đúng?

\to a . \to b = ∣ ∣ \to a ∣ ∣ . ∣ ∣ ∣ \to b ∣ ∣ ∣ . ∣ ∣ ∣ cos (\to a, \to b) ∣ ∣ ∣

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

∣ ∣ ∣ \to a . \to b ∣ ∣ ∣ = ∣ ∣ \to a ∣ ∣ . ∣ ∣ ∣ \to b ∣ ∣ ∣ . cos (\to a, \to b)

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

\to a . \to b = ∣ ∣ \to a ∣ ∣ . ∣ ∣ ∣ \to b ∣ ∣ ∣ . sin (\to a, \to b)

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

\to a . \to b = ∣ ∣ \to a ∣ ∣ . ∣ ∣ ∣ \to b ∣ ∣ ∣ . cos (\to a, \to b)

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