设数列{ a n }的前 n 项和 S n = na + n ( n -1) b ,( n =1,2,…), a 、 b 是常数且 b ≠0. (1)证明:{ a n }是等差数列. (2)证明:以( a n , -1)为坐标的点 P n ( n =1,2,…)都落在同一条直线上,并写出此直线的方程. (3)设 a =1, b = , C 是以( r , r )为圆心, r 为半径的圆( r >0),求使得点 P 1 、 P 2 、 P 3 都落在圆 C 外时, r 的取值范围.
【简答题】vt. influence sb. so that they have an unfair or unreasonable opinion about sb. or sth. 使有偏见;使有成见n. [C, U] an unreasonable opinion or feeling, esp. the feeling of not liking a particular group of peop...