Question

数学高手解答，急～

已知公差不为0的等差数列{an}满足a1，a3，a4成等比数列，Sn为{an }的前m项和，则S3－S2/S5－S3 的值为？谢谢大家了

Answer 1

设公差为d,
a3 = a1 + 2d;
a4 = a1 + 3d;
由题知：a3^2 = a1 * a4;
则：解得a1 = -4d;
(S3 - S2)/(S5 - S3) = a3/(a4+a5)=(a1+2d)/(2a1 + 7d) = 2;