设数列 {an} 的前 n 项和为 Sn，则 {an} 等差。

(1) S n4=n 2+2n, n=1,2,3

(2) S n4=n 2+ 2n +1,n=1,2,3

Successful learning is not a(n)________activity but consists of four distinct stages in a specific order

设圆 C 与圆 (x-5) 2+y2=2 ，关于 y=2x 时称，则圆 C 方程为 ( )

In 1991，while t11e economies of industrialized countries met an economic_____，the economies of developing countries were growing very fast ．

TheinteractionsbetweenChinaandtheUSwillsurelyhaveasignificant_______on.peaceandstabilityintheAsia.—Pacificregionandtheworldasawhole.