∴ take D 1 as the origin, D 1A 1 as the x axis, D 1C 1 as the y axis, and D 1D as the z axis.
Establish a spatial rectangular coordinate system as shown in the figure.
∫AB = 1, BC=2, AA 1=2, and E is the midpoint of the side BB 1.
∴d(0,0,2),a(2,0,2),e(2, 1, 1),a 1(2,0,0),c 1(0, 1,0)，
∴da=(2,0,0),ae=(0, 1,- 1),a 1e=(0, 1, 1)，
∴