我想問下呢幾條中三級既數點計(關於整數指數定律同因式分解)

1)2^(3n+1) / 8^n= 2^(3n+1) / (2^3)^n= 2^(3n+1) / 2^3n= 2^(3n+1 - 3n)= 2^1= 2
2)[3^(n+1) - 3^(n-1)] / (2 * 3^n)= [3^(n-1)] (3^2 - 1) / (2 * 3^n)= [3^(n-1)] * 4 / 3^n= (3 ^ - 1) * 4= 4/3
1) i) c²-8c-20=(c-10)(c+2)ii)y²(y - 3)² - 8y(y - 3) - 20設 y(y - 3) = c ,
則 c² - 8c - 20由 i) , = [y(y - 3) - 10] [y(y - 3) + 2]= (y² - 3y - 10) (y² - 3y + 2)= (y - 5)(y + 2) (y - 1)(y - 2)


2010-12-28 16:37:05 補充：
點解[3^(n-1)] (3^2 - 1) / (2 * 3^n)呢到既3^(n-1)會變左n-1既.唔係n+1架咩,,,(3^2-1)呢到點解會變左2-1既,唔係n-1架咩?

詳細D :

[3^(n+1) - 3^(n-1)]

先看 3^(n+1) = [3^(n - 1)] * 3^2

所以 [3^(n+1) - 3^(n-1)]

= [3^(n-1)] * 3^2 - [3^(n-1)] * 1

= [3^(n-1)] (3^2 - 1)

2010-12-28 16:39:25 補充：
給你另一做法 , 一開始可把 3^n 約掉。

[3^(n+1) - 3^(n-1)] / (2 * 3^n)

= (3^1 - 3^-1) / 2

= (3 - 1/3) / 2

= 4/3

2010-12-28 16:48:32 補充：
= (y² - 3y - 10) (y² - 3y + 2)
= (y - 5)(y + 2) (y - 1)(y - 2)
點樣由第三步可以整到最後呢個答案?!

因 y(y - 3) - 10 = y² - 3y - 10
y(y - 3) + 2 = y² - 3y + 2

所以 [y(y - 3) - 10] [y(y - 3) + 2]

= (y² - 3y - 10) (y² - 3y + 2)

2010-12-28 16:48:38 補充：
因 y² - 3y - 10 = (y - 5)(y + 2) (用交叉相乘)

y² - 3y + 2 = (y - 1)(y - 2) (用交叉相乘)

所以

= (y - 5)(y + 2) (y - 1)(y - 2)

2010-12-28 17:29:08 補充：
[3^(n+1) - 3^(n-1)] / (2 * 3^n)


= (3^n)(3 - 3^-1) / (2 * 3^n) .....為保險些,寫出這步一定不扣分。

= (3^1 - 3^-1) / 2

= (3 - 1/3) / 2

= 4/3

2010-12-28 17:39:22 補充：
謝謝你!
Thankyou!

2010-12-28 17:40:44 補充：
最後邊度??????

2010-12-28 17:49:58 補充：
計到(y - 5)(y + 2) (y - 1)(y - 2)就得,唔洗寫多句。

唔該哂上面禁多位(thx~~) .

2010-12-28 17:06:27 補充：
(3 - 1/3) / 2

= 4/3 (呢到點變4/3-.-''?!)
我上年聽唔到書.因個啊sir講得太深-.-''呢年我好比心機追架啦,不過好似仲同同班同學差好遠(我地係分班上既.我以前個班個啊sir係博士,,,,)

2010-12-28 17:11:53 補充：
/係咪分子線,錦點樣(3-1/3)之後又/2

2010-12-28 17:14:38 補充：
咩係繁分數-.-''

2010-12-28 17:15:44 補充：
喔~~除!!!!!!

2010-12-28 17:23:48 補充：
比意見係咪冇咩點數架-.-'"!?

2010-12-28 17:35:29 補充：
唔該哂.不過佢話未夠四個鐘唔可以選人做最佳-口-''

2010-12-28 17:36:50 補充：
係w0r~,最後個到洗唔洗答題?!?!

2010-12-28 17:47:16 補充：
最後個題....1ii

^ means 次方
_______________

y²(y-3)²-8y(y-3)-20
Let c be y(y-3):
(c-10)(c+2)
(y(y-3)-10)(y(y-3)+2)
(y^2-3y-10)(y^2-3y+2)
(y-5)(y+2)(y-2)(y-1)
______________
If you are experienced in factorization,you can factorize it directly.
I am a F3 student,but I learnt it in F2.

2010-12-28 15:59:49 補充：
8^n/2^3n+1
2^3n/(2^3n+1)
2^3n-3n-1
2^-1
1/2

2010-12-28 16:02:00 補充：
2(3^n)/(3^n+1)-3^(n-1))
2(3^n)/3^n(3-3^-1)
2/(8/3)
2*(3/8)
3/4

2010-12-28 17:10:00 補充：
(3 - 1/3) / 2
(8/3)/2
(8/3)除2
(8/3)x(1/2)
8/6
4/3

2010-12-28 17:12:12 補充：
http://hk.knowledge.yahoo.com/question/question?qid=7010071101779

2010-12-28 17:14:55 補充：
9/4即9除4
9x(1/4)

2010-12-28 17:16:29 補充：
好多個分數即是繁分數.

_________________
a/(b/c)
a除(b/c)
a乘(c/b)
ac/b

2010-12-28 17:17:17 補充：
= (y² - 3y - 10) (y² - 3y + 2)
= (y - 5)(y + 2) (y - 1)(y - 2)
點樣由第三步可以整到最後呢個答案?!
_________________
use cross-method.

2010-12-28 17:19:22 補充：
如果我第二題用你第二個易d既方法考試會唔會比人扣分?!
_____________________
You have to use the method likes ☂雨後陽光☀ because the question contain (Hence)(由此)