> 数学 >
等差数列{an} ,a2+a7+a10=17,a4+a5+a6+...+a14=77,ak=13,则k=
人气:298 ℃ 时间:2020-04-22 07:57:06
解答
设等差数列{an}的通项为:an = a1 +(n - 1)d,其中a1为首项,d为公差,由a2+a7+a10 = (a1 + d) + (a1 + 6d) + (a1 + 9d) = 3a1 + 16d,得:3a1 + 16d = 17-----(1)由a4+a5+a6+...+a14 = 1/2*(a4 + a14)*11 = 11*(a1 + ...
推荐
猜你喜欢
© 2026 79432.Com All Rights Reserved.
电脑版|手机版