a1=1 a2=2 a3=4 a4=7.
a2-a1=1
a3-a2=2
a4-a3=3
.
.
.
(a2-a1)+(a3-a2)+(a4-a3)+.+(an-an-1)=1+2+3+4+...+n-1
-a1+an=(n^2-n)/2
an=(n^2-n+2)/2
猜你喜欢
- 1写月亮的思乡诗句
- 2Between two classes we have a ___break.A ten-minute B ten-minutes C ten-minute's D ten-minute3'.
- 3关于两个点电荷的电势能..
- 4英文句子翻译：我只想默默得爱着你、直到我死去.
- 5I really do not know what you want to say,You want to say goodbye to me righ?waiting
- 6如果一个人的血液流动速度大于了光速,那将会怎样
- 7用英语翻译：我妈妈经常鼓励我多读报纸
- 831乘101和46乘101怎样最快算出来,他们的规律是什么
- 9问几道有关成语的语文题
- 10英语翻译：吸烟的害处 the （ ）of smoking