聯立方程 1題...urgent -20 marks-

i think there is a typing in your question,
is the second equation is x^(2) -2xy+y^(2)=5 (missing the symbol "^" )
if yes, the following is the answer


By the first equation,
(x+y)^2=3^2
x^2+2xy+y^2=9----(*)

Using (*) - second equation,
(x^2+2xy+y^2) - (x^(2) -2xy+y^(2)) = 9-5
4xy=4
xy=1

2007-06-16 17:18:02 補充：
其實係計到ga wor.如果好似你咁計, 會先計到y 個值係[3 √(9-4)]/2 或者[3-√(9-4)]/2而對應的x 會係[3-√(9-4)]/2 和[ 3 √(9-4)]/2再將佢地對應咁乘就會得出x*y=1你再試試先la,唔得再問la

2007-06-16 17:19:56 補充：
sorry, 我打錯野y 個值係[3 √(9-4)]/2 或者[3-√(9-4)]/2x 會係[3-√(9-4)]/2 和[ 3 √(9-4)]/2

2007-06-17 11:50:33 補充：
你好似計錯左個y wor我唔清楚你點計到個y 係1.5 同-5, 但就咁將佢地代入 4y^(2)-12y 4=0你會計到左手邊係 -5 或者係164 , 都唔等如右邊(即係 0 la)你再試試先la,4y^(2)-12y 4=0係 冇得factorization ga要計個數出黎就要用formular gap.s. 唔知點解都係睇唔到上次回覆個加號.

x^(2) -2xy+y^(2) =5
x^2+2xy+u^2=5+4xy
(x+y)^2=5+4xy
9=5+4xy
5+4xy=9
4xy=9-5
4xy=4
xy=1

x^(2) -2xy+y^(2) =5
x^2+2xy+u^2=5+4xy
(x+y)^2=5+4xy
9=5+4xy
4xy=4
xy=1

2007-06-16 15:37:54 補充：
呢個方法應該係最快最簡單首先每邊 4xy等佢可以做到(x y)^2出黎再代個"3"入去，咁就搞啱