例1数列{a,}首项al~3,且满足an+1- 3a__a,n。一二弓卜不(n任N‘),求一的值.a,+2、~、‘”’一a100一1一‘~’ 通常拿到题后第一反应就是求通项a。,但由题设条件解a,似乎无从下手,这时就要建立一个新数列}一五二}求解. k己n一1,解由a计1一 3a,a,+2,得a计1一1一2(a,一l) a:+2求{b Case 1 lists {a,} the first item al~3 and satisfies an+1 - 3a__a,n. One or two bows do not (n any N’), find the value of one. A, +2, ~, ’"’ a100 a 1 a’ ~’ usually get the title after the first reaction is to find a. However, the conditional solution a does not seem to be the starting point. At this time, a new sequence should be established. 152. Solve. k n n 1 and the solution is 1 to 3a, a, +2, and a is 1 One 1 - 2 (a, l) a: +2 seek {b