7.
已知点\(F_{1}(- \sqrt {5},0)\),圆\(F_{2}\):\((x- \sqrt {2})^{2}+y^{2}=16\),点\(M\)是圆上一动点,\(NF_{1}\)的垂直平分线与\(MF_{2}\)交于点\(N\).
\((1)\)求点\(N\)的轨迹方程;
\((2)\)设点\(N\)的轨迹为曲线\(E\),过点\(P(0,1)\)且斜率不为\(0\)的直线\(l\)与\(E\)交于\(A\),\(B\)两点,点\(B\)关于\(y\)轴的对称点为\(B′\),证明直线\(AB′\)过定点,并求\(\triangle PAB′\)面积的最大值.