[解題]高中指數
7^2x-(m-5)7^x+9=0
有兩正根解 求m的範圍
我想問的是
有兩根 a,b
7^a>1,7^b>1
7^a+7^b= m-5 > 2
判別式大於0
多一個條件
就是(7^a-1)(7^b-1) > 0
我想知道為什麼會出現這條件
有點像兩根之積又不像...感覺只像是解題手法...
是基於什麼原因呢?
請幫我解惑一下 謝謝
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※ 編輯: kyoooooo123 來自: 118.161.66.92 (08/13 16:37)
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