(1)α=30°. S△AOD =根3/2 ∠FOB1=∠FB1O=30°. OF=FB1=2 FB=2倍根3-2
S△OFB1=根3 △OFB1相似于△EFB 所以 S△EFB=(根3-1)^2*根3=4倍根3-6
S重=2倍根3 -S△AOD-S△EFB=6-5/2*根3
(2)若B1B=B1F ∵OB=OB1 ∠OBB1=90-α/2 ∠BFB1=30°+α 两角相等得 α=40° t=4
若BF=BB1 ∠BB1F=∠OBB1-30°=60°-α/2 两角相等得 α=20° t=2
若FB1=FB 显然不符 综上 t=2或4