6.
设\(A\),\(B\),\(C\),\(D\)为平面内的四点,且\(A(1,3)\),\(B(2,-2)\),\(C(4,1)\).
\((1)\)若\( \overrightarrow{AB}= \overrightarrow{CD}\),求\(D\)点的坐标;
\((2)\)设向量\( \overrightarrow{a}= \overrightarrow{AB}\),\( \overrightarrow{b}= \overrightarrow{BC}\),若\(k \overrightarrow{a}- \overrightarrow{b}\)与\( \overrightarrow{a}+3 \overrightarrow{b}\)平行,求实数\(k\)的值.