已知非零向量\(a\),\(b\)不共线 .
\((1)\)如果\( \overrightarrow{AB}=2a+3b \),\( \overrightarrow{BC}=6a+23b \),\( \overrightarrow{CD}=4a-8b \),求证:\(A\),\(B\),\(D\)三点共线\(;\)
\((2)\)已知\( \overrightarrow{AB}=2a+kb \),\( \overrightarrow{CB}=a+3b \),\( \overrightarrow{CD}=2a-b \),若使\(A\),\(B\),\(D\)三点共线,试确定实数\(k\)的值.