log4(x+4)+log4(x+10)=2 點計?
答案係-2 log以4做底
一題對數方程問題
2013-01-06 1:52 am
回答 (1)
2013-01-06 2:36 am
✔ 最佳答案
log₄(x+4)+log₄(x+10)=2log₄[(x+4)(x+10)]=log₄(4²)
(x+4)(x+10)=(4²)
x²+14x+40=16
x²+14x+24=0
(x+2)(x+12)=0
x=-2 or x=-12(rej.)
(rejected -12 because log₄[(-12)+4] = log₄(-8) and log can not be negative)
收錄日期: 2021-04-16 15:30:36
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20130105000051KK00282