奧數題 關於mod+solve equation 10分

2013-03-02 8:51 pm
1. 求符合 227x==1 (mod 2011) 最少正整數解

2. 已知x,y>0  求方程組

x^2/y^2 +1 /xy = 1

y/x^3 + x/y^3 = 3 的解
更新1:

the ans for question 2 is 2^1/4 and 2^3/4 !! how to get the result?

回答 (2)

2013-03-03 8:55 pm
✔ 最佳答案
Q2.
Let y = nx where n > 1
Sub. into the 1st equation
1/n^2x^2 + 1/nx^2 = 1
1/x^2 = n(1 - 1/n2) = (n^2 - 1)/n...............(1)
Sub. y = nx into the 2nd equation
n/x^2 + 1/n^3x^2 = 3
1/x^2 = 3n^3/(n^4 + 1) .....................(2)
From (1) and (2)
(n^2 - 1)/n = 3n^3/(n^4 + 1)
n^6 - 4n^4 + n^2 - 1 = 0
The only real and positive answer for n is 1.951
Sub this value into (1), we get x = 0.8338, y = nx = 1.6267.
2013-03-03 10:20 pm
Sub your solution to the question lead to different result. Can you check the question again?


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