19.(本小题满分12分)如图,四边形ABCD是正方形,EA⊥平面ABCD,AE∥BF,AE=2BF=2
(1)证明:平面EAC⊥平面EFC;
(2)若CF与平面AEC所成角为30°,求二面角F一EC-D的余弦值