求救數學高手~~解聯立方程式

2010-01-15 6:43 am
解四元聯立方程組

x^3/(2^3-1^3) + y^3/(2^3-3^3) + z^3/(2^3-5^3) w^3/(2^3-7^3) = 1 式一
 
x^3/(4^3-1^3) + y^3/(4^3-3^3) + z^3/(4^3-5^3) w^3/(4^3-7^3) = 1 式二
 
x^3/(6^3-1^3) + y^3/(6^3-3^3) + z^3/(6^3-5^3) w^3/(6^3-7^3) = 1 式三
 
x^3/(8^3-1^3) + y^3/(8^3-3^3) + z^3/(8^3-5^3) w^3/(8^3-7^3) = 1 式四
 
求 x^3 + y^3 + z^3 + w^3 = ? (已知為304)

謝謝各位大大~

回答 (3)

2010-01-15 9:17 pm
✔ 最佳答案
1. 觀察t的方程式中:
x^3/(t-1^3) + y^3/(t-3^3) + z^3/(t-5^3) w^3/(t-7^3)- 1=0
t=2^3,4^3,6^3,8^3是根
整理: x^3(t-3^3) (t-5^3) (t-7^3)+ y^3(t-1^3) (t-5^3) (t-7^3)
+z^3(t-1^3) (t-3^3) (t-7^3)+ w^3(t-1^3) (t-3^3) (t-5^3)- (t-1^3) (t-3^3) (t-5^3) (t-7^3)=0….(!)
2. f(t)= (!)=-(t-2^3) (t-4^3) (t-6^3) (t-8^3)…..(!!)
比較係數:(!)和(!!)中t^3項
得x^3 + y^3 + z^3 + w^3 +(1^3)+(3^3)+(5^3)+(7^3)
=[(2^3)+(4^3)+(6^3)+(8^3)]
故x^3 + y^3 + z^3 + w^3=800-496=304
2010-01-22 5:24 am
要...

因為(!)式子中
t^4的領導係數是-1
(!!)式要配合(!)式
所以前面要加一個-號
才會使兩多項式相等...
2010-01-15 8:29 am
w^3前面是否少一個加號?

2010-01-15 00:30:15 補充:
若是的話,答案是304沒錯!


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