設ｋ為一常數,若二次方程ｘ^2 + 14ｘ+ｋ= 0沒有實根，求ｋ的取值範圍。
ps 步驟 .. thx !*
不等式 [ form.5 ]
2007-09-11 6:21 am
回答 (2)
2007-09-11 6:30 am
方程沒有實根 -> 判別式為負
142 - 4(1)(k) < 0
196 - 4k < 0
49 - k < 0
k > 49
142 - 4(1)(k) < 0
196 - 4k < 0
49 - k < 0
k > 49
2007-09-11 6:28 am
X^2+14X+k
= X^2+14X+49+k-49
=(X+7)^2+K-49 = 0
THEN (x+7)^2 = 49-K
as (x+7)^2 > 0 so 49-k>0 and hence 49>K or k<49
= X^2+14X+49+k-49
=(X+7)^2+K-49 = 0
THEN (x+7)^2 = 49-K
as (x+7)^2 > 0 so 49-k>0 and hence 49>K or k<49
收錄日期: 2021-04-13 13:25:24
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070910000051KK04647