a1+a2+a3+a4=11,an-3+an-2+an-1+an=67
因为m+n=p+q时,am+an=ap+aq
所以a1+an=a2+a(n-1)=……
观察下标得4(a1+an)=88
sn=n(a1+an)/2=286
n=26
等差数列｛an｝中,前四项的和为21,后四项的和为67,且Sn=286,则n=多少?
等差数列｛an｝中,前四项的和为21,后四项的和为67,且Sn=286,则n=多少?
数学人气：282 ℃时间：2020-02-05 14:19:13
优质解答
我来回答
类似推荐
猜你喜欢
- 1时间就是性命,无端的空耗别人的时间,其实就是无异于谋财害命的.意思是什么.
- 2从一根横截面直径是6分米的圆柱形钢材上截下2米.已知每立方分米钢材重7.8千克,截下的这段钢材重多少千克
- 3While you reawaxy I'll remember your smile and louu you always
- 4我是一名今年报考南药研究生院的大学生.
- 5沉在水底的铁块受浮力作用吗
- 6The films were on the ground just now .(一般疑问句）
- 7--Will the new iphone cost a lot?--I ___ think so.Apple's products are usually expensive.
- 8It's a piece of cake
- 9If our parents do everything for us ,we won't learn to depend on ()AthemBusCthemslevesDourselves
- 10y=2x+1/x平方-x-2求值域,