设棱长为a延长AE,与A1C1的延长线交于F,连续B1F则平面AB1E和底面A1B1C1D1所成的角即为二面角A-B1F-A1的角.过C1作C1M垂直B1F交B1F于M,连结EM则∠EMC1为二面角A-B1F-A1的角AF=2A1C1=2√2aB1F²=A1B1²+A1F²...