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Yahoo!奇摩知識+ - 分類問答 - 科學常識 - 已解決
Yahoo!奇摩知識+ - 分類問答 - 科學常識 - 已解決
很煩的高一數學題
Jun 10th 2013, 15:15

若 f(x) 為三次多項式, 且知道 (x^2 -9)f(x) 除以 x^2 -3x -10 之餘式為 4x+8, 則
(x-1)f(x) 除以 x - 5 之餘式為 7. 對不對?

(x^2-9)f(x)=(x^2-3x-10)Q1(x)+4x+8---(1)
而照題意
(x-1)f(x)=(x-5)Q2(x)+?---(2)

那你可以把(x^2-3x-10)拆成 (x-5)(x+2)

(x^2-9)f(x)=(x-5)(x+2)Q1(x)+4x+8
代x=5進去
16f(x)=0+20+8 ---(3)
(0是因為x=5帶進去,未知的Q1(x)會乘以0等於0而被消除)

而(2)一樣代x=5
4f(x)=0+? ---(4)
(0是因為x=5帶進去,未知的Q2(x)會乘以0等於0而被消除)

仔細看看 (4)=(3)除以4
那等於後面的28除以4=7

做這種題目我建議 勇敢寫下去 拆拆看 或代代看 就會知道這題的解法

參考資料 高二的我 有問題再發問

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