题目

已知F1、F2是双曲线-y2=1的两个焦点,P在双曲线上,当△F1PF2的面积为1时,·的值为________________. 答案：0  由已知F1(,0),F2(,0),P(),PF1的斜率k1=,PF2的斜率k2=,k1k2=-1, ∴PF1⊥PF2,即=0. The premier said the nation’s development should not only promote economic growth , but also pursue social fairness and justice to      every individual’s all-round development in a free environment.          A. insure          B. ensure         C. satisfy         D. urge