求x
請列明步驟!!
更新1:
hence, solve 4^(-x)-8*4^x=2
2^x-2^(-x+3)=2,求x
回答 (2)
2008-12-14 1:46 am
✔ 最佳答案
2^x-2^(-x+3)=2x-(-x+3)=1{因為2^x-2^(-x+3)=2^1所以刪掉底數2,可得x-(-x+3)=1}
x+x-3=1
2x=4
∴x=2
2008-12-14 1:50 am
2^x - 2^(-x + 3) = 2
2^x - 82^(-x) - 2 = 0
Let 2^x = y
so y - 8/y - 2 =0
y^2 - 2y - 8 = 0
(y - 4)(y +2) = 0
y = 4 and - 2
that is
2^x = 4 = 2^2, so x = 2.
2^x = - 2 (rej.).
2^x - 82^(-x) - 2 = 0
Let 2^x = y
so y - 8/y - 2 =0
y^2 - 2y - 8 = 0
(y - 4)(y +2) = 0
y = 4 and - 2
that is
2^x = 4 = 2^2, so x = 2.
2^x = - 2 (rej.).
收錄日期: 2021-04-25 22:36:09
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20081213000051KK01341