係關於arithmetic sequence..
in a garden,red roses and white roses are planted in the following way:
(1)there is one red rose in the 1st row,three red roses in the 2nd row,five red roses in the 3rd row,and so on.
(2) in the even numbered rows (i.e. the 2nd,4th,6th,...rows),there is one white rose between every two red roses.
find
the number of white roses in the 100th row.
i need a step-by-step explanation..thank you very much!
f.5 maths
2008-09-17 9:52 am
回答 (2)
2008-09-21 5:44 am
✔ 最佳答案
rrwrwr
rwrwrwrwr
......................
w----white rose
r-----red rose
We notice that in 2nd row, red rose:3
white rose:2
in 3rd row,red rose:5
white rose:4
in nth row,red rose:2n-1
white rose:2n-2
sub n = 100
.'. white rose= 200 - 2 =198
2008-09-17 12:34 pm
A +2d = 5
A = 1
a(1) = 1W +2R > in the1st row, there is only 1white rose
a(2) = 2W +4R > in the 2nd row, there would be 2 more white rose
thet means there would be 2more rose added in each row
therefore, there would be 59white rose in the 100th row
A = 1
a(1) = 1W +2R > in the1st row, there is only 1white rose
a(2) = 2W +4R > in the 2nd row, there would be 2 more white rose
thet means there would be 2more rose added in each row
therefore, there would be 59white rose in the 100th row
收錄日期: 2021-04-13 16:04:52
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20080917000051KK00157