Question

1,-3/4,5/9,-7/16找规律,后两个数填多少

1,-3/4,5/9,-7/16找规律,后两个数填多少,谢谢

Answer 1

分子:1,-3,5,-7.....不考虑符号是:1,3,5,7,9.....奇数....a(n)=2n-1只考虑符号,1,-1,1,-1,1......偶数项为1,奇数项为-1......表达式是(-1)^(n-1)分母1,4,9,16,25.....是项数的平方.....b(n)=n^2------后两项是,9/25,-11/36第n项是(-1)^(n-1)(2n-1)/n^2-----------

Answer 2

9/25,-11/36