(2012?上海模拟)如图所示,在长方体ABCD-A1B1C1D1中,AB=1,BC=2,CC1=5,M为棱CC1上一点.(1)若C1M=32,求异面直线A1M和C1D1所成角的正切值;(2)若C1M=1,试证明:BM⊥平面A1B1M.