画出正六棱台的草图,如图示:设棱台的高为h,斜高为h′,由已知得:sinα=sin60°= 3 2 = h h′ ,设上底的半径为a,下底的半径为b,则tan60°= 3 = h 3 (b?a) ,即: h b?a =3,∵(BB′)2=h2+(b-a)2,∴ h BB′ = 3 10 10 ,又h= 3 2 h′,∴ h′ BB′ = 30 5 .