2(5^n)+25^n
___________
5^n
2).都係化簡
9^(n+1)-3^(2n)
_________________
3^(2n-1)+3^(2n+1)
更新1:
唔該2位既回答.. 不過丫sir俾我個答案唔係咁.. 佢話第1題係5^(n+1) 第2題係5/12.......
更新2:
其實我都係計到2+5^n同-3.. 唔知點解丫sir話唔係..
更新3:
to第2位答我既人;; 25^n點會變左做5^5n丫.. 唔係5^2n咩..?
f3數..指數的..化簡
2008-10-05 10:39 pm
1).化簡
2(5^n)+25^n
___________
5^n
2).都係化簡
9^(n+1)-3^(2n)
_________________
3^(2n-1)+3^(2n+1)
2(5^n)+25^n
___________
5^n
2).都係化簡
9^(n+1)-3^(2n)
_________________
3^(2n-1)+3^(2n+1)
回答 (2)
2008-10-05 10:57 pm
1). 2(5^n)+25^n/5^n
=2(5^n)+5^5n/5^n
=5^n(2+7)/5^n
= 2+7
=9
2). 9^(n+1)-3^(2n)/3^(2n-1)+3^(2n+1)
=3^3n+3-2n/3^2n-1+2n+1
=3^n+3/3^4n
=3^n+3-4n
=3^3-3n
=3^3(1-n)
2008-10-05 14:59:07 補充：
CORR.
1). 2(5^n)+25^n/5^n
=2(5^n)+5^5n/5^n
=5^n(2+5)/5^n
= 2+5
=7
2008-10-06 22:50:33 補充：
orry,之前全錯
25^n=5^2n
1.2(5^n)+25^n
___________
5^n
=[ 2(5^n)+(5^2)^n ]/5^n
=[2(5^n)+(5^n)(5^n)]/5^n
=5^n(2+5^n)/5^n
=2+5^n
2008-10-06 22:50:47 補充：
但你sir話:5^(n+1)
let n=1
代返落 2(5^n)+25^n
___________
5^n
ans=7
而我個ans:2+5^n
化返都=7
2008-10-06 22:50:59 補充：
2. 9^(n+1)-3^(2n)
_________________
3^(2n-1)+3^(2n+1)
=9^n*9-9^n / (3^2n)/3+(3^2n)3
=9n(9-1) / 9^n/3+(9^n*3)
=9^n(8) / 9^n(1/3+3)
=8 / 1/3+3
=2.4
2008-10-06 22:51:09 補充：
但你sir話: 5/12
let n=1落條式
ans=2.4
=2(5^n)+5^5n/5^n
=5^n(2+7)/5^n
= 2+7
=9
2). 9^(n+1)-3^(2n)/3^(2n-1)+3^(2n+1)
=3^3n+3-2n/3^2n-1+2n+1
=3^n+3/3^4n
=3^n+3-4n
=3^3-3n
=3^3(1-n)
2008-10-05 14:59:07 補充：
CORR.
1). 2(5^n)+25^n/5^n
=2(5^n)+5^5n/5^n
=5^n(2+5)/5^n
= 2+5
=7
2008-10-06 22:50:33 補充：
orry,之前全錯
25^n=5^2n
1.2(5^n)+25^n
___________
5^n
=[ 2(5^n)+(5^2)^n ]/5^n
=[2(5^n)+(5^n)(5^n)]/5^n
=5^n(2+5^n)/5^n
=2+5^n
2008-10-06 22:50:47 補充：
但你sir話:5^(n+1)
let n=1
代返落 2(5^n)+25^n
___________
5^n
ans=7
而我個ans:2+5^n
化返都=7
2008-10-06 22:50:59 補充：
2. 9^(n+1)-3^(2n)
_________________
3^(2n-1)+3^(2n+1)
=9^n*9-9^n / (3^2n)/3+(3^2n)3
=9n(9-1) / 9^n/3+(9^n*3)
=9^n(8) / 9^n(1/3+3)
=8 / 1/3+3
=2.4
2008-10-06 22:51:09 補充：
但你sir話: 5/12
let n=1落條式
ans=2.4
2008-10-05 10:49 pm
收錄日期: 2021-04-23 20:43:35
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20081005000051KK01293