二元一次方程(好緊急，唔該大家幫幫忙)

3(a) x-y=1 ---1
x+y=1 ---2
1+2: 2x=2
x=1
sub this into 1
1-y=1
y=0
x=1,y=0

(b)x-y=-2 ---1
2x+y=5 ---2
1+2: 3x=3
x=1
sub this into 1
1-y=-2
-y=-3
y=3
x=1 y=3

(c)x+y=1 ---1
2x-y=2 ---2
1+2: 3x=3
x=1
sub this into 1
1+y=1
y=0
x=1,y=0

2008-10-19 18:08:23 補充：
5. (a)2x+5y=31 ---1
4x+6y=42 ---2
1+2: 4x+10y=62 ---1'
1'-2: 4y=20
y=5
sub this into 1
2x+25=31
2x=6
x=3
x=3,y=5

2008-10-19 18:08:30 補充：
(b)2x+3y-14=0 ---1
2x-3y-2=0 ---2
1 becomes: 2x+3y=14 ---1'
2 becomes: 2x-3y=2 ---2'
1'-2': 6y=12
y=2
sub this into 1'
2x+6=14
2x=8
x=4
x=4,y=2

2008-10-19 18:12:48 補充：
(c)15x-2y-28=0 ---1
25x+3y-53=0 ---2
1 becomes: 15x-2y=28 ---1'
2 becomes: 25x+3y=53 ---2'
1'*3: 45x-6y=84 ---1"
2'*2: 50x+6y=106 ---2"
1"+2": 95x=190
x=2
sub this into 1'
30-2y=28
-2y=-2
y=1

因為太多..所以寫o左o係紙再up上黎

http://farm4.static.flickr.com/3210/2954328752_f743e5dd28.jpg?v=0