题目

F, I'd like to thank all those people who helped make the conference such a success. 答案：【1】Finally18．已知数列{an}是等差数列．且a1=2．a1+a2+a3=12．（1）求数列{an}的通项公式．（2）令bn=xan（x＞0），求数列{bn}的前n项和（用x表示）．