4.
如图所示,在三棱柱\(ABC-A\)\({\,\!}_{1}\)\(B\)\({\,\!}_{1}\)\(C\)\({\,\!}_{1}\)中,底面\(\triangle \)\(ABC\)为正三角形,且侧棱垂直于底面\(.AB=\)\(2\),\(AA\)\({\,\!}_{1}\)\(=\)\(2\),从顶点\(B\)沿棱柱侧面\((\)经过棱\(AA\)\({\,\!}_{1})\)到达顶点\(C\)\({\,\!}_{1}\),与\(AA\)\({\,\!}_{1}\)的交点记为\(M.\)求:
\((1)\)三棱柱\(ABC-A\)\({\,\!}_{1}\)\(B\)\({\,\!}_{1}\)\(C\)\({\,\!}_{1}\)侧面展开图的对角线长\(;\)
\((2)\)从\(B\) 经过\(M\) 到\(C\)\({\,\!}_{1}\)的最短路线长及此时\( \dfrac{{A}_{1}M}{AM} \)的值.