數學的指數問題

2008-08-23 11:35 am
3^x = 9
我知x = 3
但係點列式??

9^-x = 1/27
find x.

Let a 唔等於0. solve for x
a^(x-5) = a^4

a^(3x) = a^9

最緊要列式, d式點寫我全部唔記得左!!

回答 (2)

2008-08-23 6:08 pm
✔ 最佳答案
3^x = 9
3^x = 3^2
x = 2(因為數學入面ge指數如果兩邊最後個底:3相同,可以只睇個指數)


9^-x = 1/27
(3^2)^-x = 1/(3^3).....(將兩邊ge野全部變指數,再將個底整做相同)
3^-2x = 3^-3
-2x = -3(原因同第1條)
x = 3/2


Let a 唔等於0. solve for x
a^(x-5) = a^4
x-5 = 4
x = 9

a^(3x) = a^9
3x = 9
x=3
參考: 當然係自己la
2008-08-23 5:35 pm
第一
個x=2
指數唔係x數
係佢本身個數自x幾多次
3^x=9
x=2
3x3=9



仲有...你計次方可用log黎計

9^-x = 1/27
find x.
9log-x=log1/27
之後除左佢就ok....
自己用計數機禁la


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