Phát biểu nào sau đây là đúng? A. ( a + b ) → u = → u + b → u ∀ → u , ∀ b ∈ R . B. ( a + b ) → u = a → u + → u ∀ → u , ∀ a ∈ R .

\(({\rm{a}} + {\rm{b}})\overrightarrow {\rm{u}} = \overrightarrow {\rm{u}} + {\rm{b}}\overrightarrow {\rm{u}} \forall \overrightarrow {\rm{u}} ,\forall {\rm{b}} \in \mathbb{R}.\)

\(({\rm{a}} + {\rm{b}})\overrightarrow {\rm{u}} = {\rm{a}}\overrightarrow {\rm{u}} + \overrightarrow {\rm{u}} \forall \overrightarrow {\rm{u}} ,\forall {\rm{a}} \in \mathbb{R}.\)

\(({\rm{a}} + {\rm{b}})\overrightarrow {\rm{u}} = {\rm{a}}\overrightarrow {\rm{u}} - {\rm{b}}\overrightarrow {\rm{u}} \forall \overrightarrow {\rm{u}} ,\forall {\rm{a}},{\rm{b}} \in \mathbb{R}.\)

\(({\rm{a}} + {\rm{b}})\overrightarrow {\rm{u}} = {\rm{a}}\overrightarrow {\rm{u}} + {\rm{b}}\overrightarrow {\rm{u}} \forall \overrightarrow {\rm{u}} ,\forall a,b \in \mathbb{R}.\)