The sum of the first n positive odd integers are given as:
S=1+3+5+......+(2n-1)=n^2
(a)How many integers are there in 1,3,5,7,......,13?
(b)Find the sum of 1+3+5+7+......13
(c)Find the sum of 15+17+19+.....+29.
Steps and explanations must be clearly shown.Noted with thanks!!! :)
Uses of formulae
2013-01-14 3:16 am
回答 (2)
2013-01-14 3:38 am
✔ 最佳答案
(a) 1, 3, 5, 7, 9, 11, 13 are integersThere are 7 integers.
(b) 2n-1 = 13
n = 7
7^2 = 49
(c) 2n-1 = 29 2n-1 = 13
n = 15 n = 7
15^2 - 7^2
= 225 - 49
= 176
2013-01-14 8:55 am
a)
13=2(7) -1
there are 7 intergers in 1,3,5,7,......,13
b)
1+3+5+7+,......+13 = 7² = 49
c)
15+17+19+...+29 (note: 29= 2*15-1)
= (1+3+5+7+...+29) - (1+3+5+7+...+13)
= 15²-7²
= 176
13=2(7) -1
there are 7 intergers in 1,3,5,7,......,13
b)
1+3+5+7+,......+13 = 7² = 49
c)
15+17+19+...+29 (note: 29= 2*15-1)
= (1+3+5+7+...+29) - (1+3+5+7+...+13)
= 15²-7²
= 176
參考: 我本人
收錄日期: 2021-04-20 21:37:41
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