题目: △ABC中已知BC=1,AC=2,A=30°,则AB等于( )A.6-22B.6+22C.6+22或6-22D.3-22 答案: ∵BC=1,AC=2,cosA=32,∴由余弦定理得:BC2=AC2+AB2-2AC•ABcosA,即1=2+AB2-22•AB•32,解得:AB=6+22或6-22.故选C