a maths question

1
x+2y=-3 _1
-2x-4y=6 _2
_1*2:
2x+4y=-6 _3
since _3+_2=0, therefore no solutions

2
2.5x-3y-2=0 _1
15x-9y-4=0 _2
from _1:
2.5x-3y=2
15x-18y=12 _3
_3-_2:
-9y=12
y=-4/3
sub. y=-4/3 into _2:
15x-9(-4/3)-4=0
15x+12-4=0
15x=-8
x=-8/15
therefore x=-8/15, y=-4/3

2007-07-17 15:23:19 補充：
sorry, both of them have no solutions

2007-07-17 15:23:56 補充：
I should say there are infinity solutions of them

2007-07-17 15:26:10 補充：
You will understand if you draw a graph of those equations.both of each question are the same line with the same slope,no intersection

1.
x+2y=-3---<1 >
-2x-4y=6---<2>

<1> x (-2):

-2x - 4y = 6

hence,there are infinity combinations of (x,y)



2.
5x-3y-2=0----<1>
15x-9y-4=0---<2>

<1> x 3

15x - 9y - 6 = 0---<3 >

comparing <2> and <3>

there has no combination of (x,y) satisfy the given equations.