soofuk

做完

thx:D

[ 本帖最後由 soofuk 於 2011-3-3 10:49 PM 編輯 ]

Aoren

兩條都係用 a^(m+n) = (a^m) (a^n)

firoazen

Try to let n^x=a
you will find that its easier to solve it.

Aoren

always try a^(m+n) = (a^m)(a^n)
then you can see a quadratic equation

soofuk

引用:

原帖由 Aoren 於 2011-3-1 06:49 PM 發表
always try a^(m+n) = (a^m)(a^n)
then you can see a quadratic equation

引用:

原帖由 firoazen 於 2011-3-1 06:02 PM 發表 [url=redirect.php?goto=findpost&pid=2985615&ptid=165574][/url]
Try to let n^x=a
you will find that its easier to solve it.

都整唔倒個底數一樣 好似29 咁個320

Aoren

留意4^x 汁埋一齊
再combine埋一齊, 就會出到4^x = 4^b
最後就是x = b

kaisanglo

30.(2^x)(4)-6(2^x)(2^-1)=8(2^x)(4-6(2^-1))=8
29.將4^x轉去左邊 再抽4^x
之後下面個2條都係用一元二次方程

[ 本帖最後由 kaisanglo 於 2011-3-1 08:14 PM 編輯 ]

Aoren

29, 30 都係將d野放埋一邊
31, 32 都係quadratic equations

kin1205

29同30做法一樣, 31同32做法一樣..
做2題比你參考下..

29)
4^(x-1) = 320 - 4^x
(1/4)(4^x) = 320 - 4^x
(5/4)(4^x) = 320
4^x = 256
4^x = 4^4
x = 4

31)
3^(2x+1) +11(3^x) - 4 = 0
(3)(3^2x) +11(3^x) - 4 =0
3(3^x)^2 + 11(3^x) - 4 = 0
[ 3(3^x)-1 ][ (3^x) +4 ] = 0
3(3^x) - 1 = 0  or 3^(x)+4 = 0 (reject)
3^x = 1/3
x = -1

soofuk

唔該晒先 今晚要計晒佢