UC知道How Many Elements
来源：百度知道 编辑：UC知道 时间：2024/05/09 17:51:57
How Many Elements
{4,13,22,31,...,400}
How many terms would be in the above set of numbers?
{4,13,22,31,...,400}
How many terms would be in the above set of numbers?
45.
let A1=4 An=400, from the set given we can deduce that Ak=4+9(k-1).
Plug in Ak=400 so that 9k-5=400 where k=45
So the elements in the set is from A1 to A45 which means there are 45 elements.
45
40
45
算法如下：
该集合中的数为一等差数列：
a1=4,d=9,an=400
an=a1+(n-1)d
即400＝4＋9（n-1）
解得
n=45