Re: [中學] 解三元二次方程
※ 引述《haolihy (好厲害)》之銘言：
: p* (x+y) =221
: p* (1+x^2) =281
: p* (1+y^2) =209
: 求x, y, p ?
p* (x+y) =221 -----------------(1)
p* (1+x^2) =281 -----------------(2)
p* (1+y^2) =209 -----------------(3)
(2)-(3) p(x-y)(x+y)
--------- = ------------------- = 72/221
(1) p(x+y)
x-y =72/221
x=y+72/221
1+(y+72/221)^2
(2)/(3) ==> -------------------- =281/209
1+y^2
1+y^2 + 2(72/221)y+ (72/221)^2 = 281/209 (1+y^2)
72y^2/209 -144y/221 + 2433096/10207769 =0
代公式 y=0.495754 或 1.39565
選(1)/(3)比較好看點
(2y+72/221)/(1+y^2) =221/209
主要數字出得好醜
帶回
{x,y,p} ={0.8215 , 0.49575 , 167.767}
{x,y,p} ={1.72144 , 1.39565 , 70.8995}
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◆ From: 118.169.82.226
※ 編輯: suker 來自: 118.169.82.226 (03/02 19:18)
推
03/02 19:17, , 1F
03/02 19:17, 1F