數學聯合方程

x + y = -4______(1)
2x - 4y = 1______(2)

From(1)
x = -4 - y______(3)

Sub. (3) into (2)
2(-4 - y) - 4y = 1
-8 - 2y - 4y = 1
-8 - 6y = 1
-6y = 1+8
y = -9/6
y = -3/2

Sub. y = -3/2 into (3)
x = -4 - (-3/2)
x = -4 + 3/2
x = -8/2 + 3/2
x = -5/2

So, x = - 5/2 , y = -3/2

2009-01-04 21:58:39 補充：
呢條根本唔止呢個答案!!!

2009-01-04 22:06:35 補充：
若
3x + 5y = 4______(1)
x + y = -4______(2)
........
x = -12 , y = 8

2009-01-04 22:11:59 補充：
若
3x + 5y = 4______(1)
2x - 4y = 1______(2)
........
x = 21/22 , y = 5/22

2009-01-04 22:12:51 補充：
呢題總共有三個解喎......

x+y=4
y=4-x

3x+5(4-x)=4
3x+20-5x=4
-2x=-16
-x=-8
x=8

x+y=4
8+y=4
8-4=-y
4=-y
y=-4


唔知岩唔岩架...我d數唔係好勁...

2個未知數用其中2條式都可以解聯合方程