教教我!!!thanks !!
Given an arithmetic progression 50,46,42,.....,-62, find
(a.) the number of terms that is in the progression
(b.) the smallest positive term
Arithmetic Progression A.S !!!!
2008-06-06 7:51 am
回答 (2)
2008-06-06 8:11 am
✔ 最佳答案
(A)By
T(n)=a+(n-1)d
-62=50+(n-1)(-4)
4n-4=112
n=116/4=29
So there are 29 terms in the progression
(b)
Let
a+(n-1)d>0
50+(n-1)(-4)>0
50>4(n-1)
13.5>n
Let n=13
the smallest positive term
=50-4(13-1)
=2
2008-06-06 00:11:49 補充：
> means >
2008-06-06 8:17 am
睇返a)
好明顯個AS每個term都係減4
所以第一個term就係50
二就係50-4=46
三就就50-4-4=42
即係第n個term就要減4(n-1)
好明顯50要減112先至到62
即係要減28個4
所以(n-1)係28
n=29
總共有29個terms
b)睇返個sequence
就會知道成個sequence裡面最細果個positive number係2
50,46,42,......,6 , 2 , -2 , -4.......,-62
而50-48=2
即係4(n-1) = 48
n-1 = 12
n=13
所以b係13
好明顯個AS每個term都係減4
所以第一個term就係50
二就係50-4=46
三就就50-4-4=42
即係第n個term就要減4(n-1)
好明顯50要減112先至到62
即係要減28個4
所以(n-1)係28
n=29
總共有29個terms
b)睇返個sequence
就會知道成個sequence裡面最細果個positive number係2
50,46,42,......,6 , 2 , -2 , -4.......,-62
而50-48=2
即係4(n-1) = 48
n-1 = 12
n=13
所以b係13
參考: me
收錄日期: 2021-04-26 13:06:21
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080605000051KK02988