8.如图,在三棱柱ABC−A1B1C1ABC-A_{1}B_{1}C_{1}ABC−A1B1C1中,AB=AC=2AB=AC=2AB=AC=2,AA1=3AA_{1}=3AA1=3,∠BAC=60∘\angle BAC=60\circ∠BAC=60∘,∠A1AC=∠A1AB=120∘\angle A_{1}AC=\angle A_{1}AB=120\circ∠A1AC=∠A1AB=120∘,B1CB_{1}CB1C与BC1BC_{1}BC1的交点为MMM,则AM=(AM=(AM=( )))