在数列{a n }中,如果存在非零常数T,使得a m+T =a m 对任意正整数m均成立,那么就称{a n }为周期数列,其中T叫做数列{a n }的周期.已知数列{x n }满足x n+1 =|x n -x n-1 |(n≥2,n∈N * ),且x 1 =1,x 2 =a(a≤1,a≠0),当数列{x n }周期为3时,则该数列的前2007项的和为______
【简答题】Today,people all over the world are moving out of small villages in the country to go and live in big,noisy cities.They are moving from the peaceful hills,mountains,fields,rivers and streams of the co...
【简答题】Today, people all over the world are moving out of small villages in the country to go and live in big noisy cities . They are moving from the peaceful hills, mountains, fields, rivers and streams of ...
【简答题】Today, people all over the world are moving out of small villages in the country to go and live in big, noisy cities. They are moving from the peaceful hills, mountains, fields, rivers and streams of ...