英文数列题目 In a particular arichmetic progression,the sum of the 9th and 10th terms is-64.Also
问题描述：
英文数列题目 In a particular arichmetic progression,the sum of the 9th and 10th terms is-64.Also
In a particular arichmetic progression,the sum of the 9th and 10th terms is-64.Also,the difference between the sum of the first 5 terms and 2 times the fifth term is-49.What is the sum of the first 30 terms?
答
先翻译一下吧,在一个等差数列中,第九项和第十项的和是-64,前五项的和与第五项的两倍数之间相差-49,求前三十项的和.作为文科生表示压力很大~但还是解一下吧~首项为-15,公差是-2,前三十项的和是-1320,a9+a10=-64 -----...