8.
如图,已知圆\(O\):\(x\)\({\,\!}^{2}\)\(+y\)\({\,\!}^{2}\)\(=4\)与坐标轴交于\(A\)\({\,\!}_{1}\),\(A\)\({\,\!}_{2}\),\(B\)\({\,\!}_{1}\),\(B\)\({\,\!}_{2}\).
\((1)\)点\(Q\)是圆\(O\)上除\(A_{1}\),\(A_{2}\)外的任意点\((\)如图\(1)\),\(A_{1}Q\),\(A_{2}Q\)与直线\(y+3=0\)交于不同的两点\(M\),\(N\),求线段\(MN\)长度的最小值;
\((2)\)点\(P\)是圆\(O\)上除\(A_{1}\),\(A_{2}\),\(B_{1}\),\(B_{2}\)外的任意点\((\)如图\(2)\),直线\(B_{2}P\)交\(x\)轴于点\(F\),直线\(A_{1}B_{2}\)交\(A_{2}P\)于点\(E.\)设\(A_{2}P\)的斜率为\(k\),\(EF\)的斜率为\(m\),求证:\(2m-k\)为定值.