Cho vectơ $\overrightarrow b \ne \overrightarrow 0 ,{\rm{ }}\overrightarrow a  =  - 2\overrightarrow b {\rm{ }}{\rm{, }}\overrightarrow c  = \overrightarrow a  + \overrightarrow b $. Khẳng định nào sau đây sai?

\(\overrightarrow {AI}  = \dfrac{1}{4}\left( {\overrightarrow {AB}  + \overrightarrow {AC} } \right).\)

\(\overrightarrow {AI}  = \dfrac{1}{4}\left( {\overrightarrow {AB}  - \overrightarrow {AC} } \right).\)

\(\overrightarrow {AI}  = \dfrac{1}{4}\overrightarrow {AB}  + \dfrac{1}{2}\overrightarrow {AC} .\)

\(\overrightarrow {AI}  = \dfrac{1}{4}\overrightarrow {AB}  - \dfrac{1}{2}\overrightarrow {AC} .\)

\(\overrightarrow {AG}  = \dfrac{2}{3}\left( {\overrightarrow {AB}  + \overrightarrow {AC} } \right).\)

\(\overrightarrow {AG}  = \dfrac{1}{3}\left( {\overrightarrow {AB}  + \overrightarrow {AC} } \right).\)

\(\overrightarrow {AG}  = \dfrac{1}{3}\overrightarrow {AB}  + \dfrac{2}{2}\overrightarrow {AC} .\)

\(\overrightarrow {AI}  = \dfrac{2}{3}\overrightarrow {AB}  + 3\overrightarrow {AC} .\)

\(\overrightarrow {IB}  + 2\overrightarrow {IC}  + \overrightarrow {IA}  = \overrightarrow 0 .\)

\(\overrightarrow {IB}  + \overrightarrow {IC}  + 2\overrightarrow {IA}  = \overrightarrow 0 .\)

\(2\overrightarrow {IB}  + \overrightarrow {IC}  + \overrightarrow {IA}  = \overrightarrow 0 .\)

\(\overrightarrow {IB}  + \overrightarrow {IC}  + \overrightarrow {IA}  = \overrightarrow 0 .\)

\(a.\)    

\(\left( {1 + \sqrt 2 } \right)a.\)

\(a\sqrt 5 .\)

\(2a\sqrt 2 .\)

\(\overrightarrow {AC}  + \overrightarrow {BD}  = 2\overrightarrow {BC} .\)

\(\overrightarrow {AC}  + \overrightarrow {BC}  = \overrightarrow {AB} .\)

\(\overrightarrow {AC}  - \overrightarrow {BD}  = 2\,\overrightarrow {CD} .\)

\(\overrightarrow {AC}  - \overrightarrow {AD}  = \overrightarrow {CD} .\)

\(2\overrightarrow {MA}  + \overrightarrow {MB}  - 3\overrightarrow {MC}  = \overrightarrow {AC}  + 2\overrightarrow {BC} .\)

\(2\overrightarrow {MA}  + \overrightarrow {MB}  - 3\overrightarrow {MC}  = 2\overrightarrow {AC}  + \overrightarrow {BC} .\)

\(2\overrightarrow {MA}  + \overrightarrow {MB}  - 3\overrightarrow {MC}  = 2\overrightarrow {CA}  + \overrightarrow {CB} .\)

\(2\overrightarrow {MA}  + \overrightarrow {MB}  - 3\overrightarrow {MC}  = 2\overrightarrow {CB}  - \overrightarrow {CA} .\)

\(2\vec a + \vec b,\,\,\vec a + 2\vec b.\)

\(2\vec a - \vec b,\,\,\vec a - 2\vec b.\)

\(5\vec a + \vec b,\,\, - \,10\,\vec a - 2\vec b.\)

\(\vec a + \vec b,\,\,\vec a - \vec b.\)