1.
已知\(A\),\(B\),\(C\)三点不共线,对平面\(ABC\)外的任一点\(O\),若点\(M\)满足\(\overrightarrow{OM}= \dfrac{1}{3}(\overrightarrow{OA}+\overrightarrow{OB}+\overrightarrow{OC}).\)
\((1)\)判断\(\overrightarrow{MA}\),\(\overrightarrow{MB}\),\(\overrightarrow{MC}\)三个向量是否共面;
\((2)\)判断点\(M\)是否在平面\(ABC\)内.