註冊日: 2004-07-28 發表數: 143 University of Texas at Austin
誰可以幫幫忙
_________________ Atra esternī ono thelduin Mor'ranr līfa unin hjarta onr Un du evarīnya ono varda. May good fortune rule over you Peace live in your heart And the stars watch over you.
2004-10-03 17:56
訪客
Re: 誰可以幫幫忙
可以從3數成等比有何關係 與根與係數去思考
2004-10-03 20:29
訪客
Re: 誰可以幫幫忙
b^3=a^3*c
2004-10-03 23:34
訪客
Re: 誰可以幫幫忙
let f(x)=x^3+ax^2+bx+c=0 ----(1) ∵f(x)有三實數根..且為三次多項式 ∴f `(x)=3x^2+2ax+b=0 -----(2) f ``(x)=6x+2a=0 -----(3) by (3) then x= -a/3 ---(4) by (2),(4) then b=(a^2)/3 ----(5) by (1),(4),(5) then c=(a^3)/27 ∴ a=a , b=(a^2)/3, c=(a^3)/27 # by 前墮落學生
2004-10-04 13:23
訪客
Re: 誰可以幫幫忙
不好意思....沒注意到三個根成等比級數... by 前墮落的學生
2004-10-04 13:59
訪客
Re: 誰可以幫幫忙
引文:
寫道: let f(x)=x^3+ax^2+bx+c=0 ----(1) ∵f(x)有三實數根..且為三次多項式 ∴f `(x)=3x^2+2ax+b=0 -----(2) f ``(x)=6x+2a=0 -----(3)
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