f3數..指數的..化簡

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

As follow AS~~~

圖片參考：http://www.photo-host.org/img/281519screenhunter_02_oct._05_14.45.gif