8.
四边形\(ABCD\)中,\(\overrightarrow{AB}=(6,1), \overrightarrow{BC}=(x,y), \overrightarrow{CD}=(-2,-3) \).
\((1)\)若\(\overrightarrow{BC}/\!/DA \),试求\(x\)与\(y\)满足的关系式;
\((2)\)满足\((1)\)的同时又有\(\overrightarrow{AC}⊥ \overrightarrow{BD} \),求\(x\),\(y\)的值及四边形\(ABCD\)的面积.