✔ 最佳答案
6a) 5x+3y+6=0........(1)
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3x-2y-23=0........(2)
(1)*3-(2)*5
15x+9y+18-15x+10y+115=0
19y=-133
y=-7
sub into (1)
5x+3(-7)+6=0
5x-21+6=0
5x-15=0
x=3
8a) 2(x+y)-3x=4.....(1)
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3(x-y)+5y=12....(2)
From (1)
2x+2y-3x=4
2y-x=4........(3)
From (2)
3x-3y+5y=12
3x+2y=12........(4)
(3)-(4)
2y-x-3x-2y=4-12
-4x=-8
x=2
sub into (3)
2y-2=4
y=6/2
y=3
9a) 3x-2y=2........(1)
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x- y/2 = -4.........(2)
(2)*4
4x-2y=-16........(3)
(1)-(3)
3x-2y-4x+2y=2+16
-x=18
x=-18
sub into (1)
3(-18)-2y=2
-54-2y=2
2y=-56
y=-28
r^2-rs-rt+st
=r(r-s)+t(-r+s)=r(r-s)-t(r-s)=(r-s)(r-t)=(r-t)(r-s)
2010-10-08 00:14:51 補充：
唔好意思, 用左 method of elimination!!
2010-10-08 11:43:00 補充：
6a) 5x+3y+6=0…..(1)
｛
3x-2y-23=0………….(2)
From (1) 3y=-5x-6
y=(-5x-6)/3
sub y into (2)
3x-2(-5x-6)/3-23=0
9x+10x+12-69=0
19x=57
x=3
y=[(-5)(3)-6]/3
=-21/3
=-7
8a) 2(x+y)-3x=4………(1)
｛
3(x-y)+5y=12……..(2)
From (1),
2x+2y-3x=4
2y-x=4
x=2y-4
sub x into (2)
3(2y-4-y)+5y=12
3y-12+5y=12
8y=24
y=3
x=2y-4
=6-4
=2
2010-10-08 11:44:27 補充：
9a) 3x-2y=2…..(1)
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x- y/2 = -4…….(2)
From (2)
x=-4+y/2
sub x into (1)
3(-4+y/2)-2y=2
-24+3y-4y=4
y=-28
x=-4+y/2
=-4-28/2
=-4-14
=-18
用番method of substitution 啦, 自己 check 啦
