A:ad+bc
B:c(b﹣d)+d(a﹣c)
C:ad+c(b﹣d)
D:ab﹣cd
如图,在三棱柱ABC﹣A1B1C1中,四边形A1ABB1为菱形,∠A1AB=45°,四边形BCC1B1为矩形,若AC=5,AB=4,BC=3
(1)求证:AB1⊥面A1BC;(2)求二面角C﹣AA1﹣B的余弦值.
—Oh, no. It's No. 2 Bus. We should take No. 11.