7.
\((1)\)已知过点\(M(-3,0)\)的直线\(l\)被圆\({x}^{2}+(y+2{)}^{2}=25 \)所截得的弦长为\(8\),那么直线\(l\)的方程为________.
\((2)\)已知圆\(C_{1}\):\(x^{2}+y^{2}+2x+8y-8=0\)与圆\(C_{2}\):\(x^{2}+y^{2}-4x-4y-2=0\)相交,则圆\(C_{1}\)与圆\(C_{2}\)的公共弦长为______________.
\((3)\) 过点\(A(0,2)\),\(B(-2,2)\),且圆心在直线\(x-y-2=0\)上的圆的方程是 .
\((4)\) 已知圆的方程\((x-2)^{2}+y^{2}=1\),过圆外一点\(P(3,4)\)作一条直线与圆交于\(A\),\(B\)两点,那么\(\overrightarrow{PA}\cdot \overrightarrow{PB}=\)________.