连结AD1和A1D,相交于E,
则AD1⊥A1D,
CD⊥平面ADD1A1,
AD1∈平面ADD1A1,
故AE⊥CD,
CD∩A1D=D,
故AE⊥平面A1DCB1,
则〈ACE就是AC与平面A1B1CD所成角,
设棱长为1,
AD1=√2,
AE=√2/2,
AC=√2,
sin