10.如图所示,已知ABCD-A1B1C1D1是棱长为a的正方体,E,F分别是棱AA1和CC1中点,求四棱锥A1-EBFD1的体积.
[解析] ∵EB=BF=FD1=D1E=
=a,且EB∥FD1,ED1∥BF,
∴四边形EBFD1为菱形.又△EFB≌△EFD1,且三棱锥A1-EFB和A1-EFD1等高,
∴VA1-EFB=VA1-EFD1,
∴VA1-EBFD1=2VA1-EFB=2VF-EA1B.
而S△EA1B=××a=,F到面EA1B的距离为a,
∴VF-EA1B=××a=,
∴VA1-EBFD1=.
=a,且EB∥FD1,ED1∥BF,
∴四边形EBFD1为菱形.又△EFB≌△EFD1,且三棱锥A1-EFB和A1-EFD1等高,
∴VA1-EFB=VA1-EFD1,
∴VA1-EBFD1=2VA1-EFB=2VF-EA1B.
而S△EA1B=××a=,F到面EA1B的距离为a,
∴VF-EA1B=××a=,
∴VA1-EBFD1=.