四棱柱\(ABCD-A_{1}B_{1}C_{1}D_{1}\)的底面是平行四边形,\(M\)是\(AC\)与\(BD\)的交点\(.\)若\( \overrightarrow{AB}= \overrightarrow{a}\),\( \overrightarrow{AD}= \overrightarrow{b}\),\( \overrightarrow{AA_{1}}= \overrightarrow{c}\),则\( \overrightarrow{C_{1}M}\)可以表示为\((\) \()\)