题目

若椭圆b2x2+a2y2=a2b2(a>b>0)的左焦点为F,右顶点为A,上顶点为B,且离心率为,求∠ABF. 答案：∠ABF=90°. 解析:椭圆方程为=1(a>b>0), 则F(-c,0)、A(a,0)、B(0,b), |AB|=,|AF|=a+c,|BF|=a. ∴cos∠ABF= . ∵e==,∴a2-ac-c2=0. ∴cos∠ABF=0. ∴∠ABF=90°._______ the ointment to the wound, the nurse carefully wrapped it up with a bandageA.TreatedB.Having treatedC.AppliedD.Having applied