6.
如图所示,在\(\triangle ABC\)中,\(D\)、\(F\)分别是\(BC\)、\(AC\)的中点,\(\overrightarrow{AE}=\dfrac{2}{3}\overrightarrow{AD}\),\(\overrightarrow{AB}=a\),\(\overrightarrow{AC}=b\).
\((1)\)用\(a\),\(b\)表示向量\(\overrightarrow{AD}\)、\(\overrightarrow{AE}\)、\(\overrightarrow{AF}\)、\(\overrightarrow{BE}\)、\(\overrightarrow{BF}\);
\((2)\)求证;\(B\)、\(E\)、\(F\)三点共线.