(1)求证:EF⊥DC;
(2)求证:GF∥平面PAD;
(3)求点G到平面PAB的距离.
12.如图所示,在三棱柱ABC-A1B1C1中,侧棱AA1⊥底面ABC,AB=AC=1,AA1=2,∠B1A1C1=90°,D为BB1的中点.
求证:AD⊥平面A1DC1.