聯立方程的問題~數學高手入

2x-y+4=25-3x+2y=12
2x-y+4=12
y=2x+4-12

25-3x+2y=12
25-3x+2(2x+4-12)=12
25-3x+4x-16=12
-3x+4x=12+16-25
x=3
代入y=2x+4-12............y=2*3+4-12
y=6+4-12=-2

2(1-2x)-(3y-2)=9
2-4x-3y+2=9
4x=2+2-9-3y
4x=-5-3y
x= (-5-3y)/4

3(x-2)+2(4y+3)=2
3x-6+8y+6=2
3x+8y=2
3(-5-3y)/4+8y=2
-15-9y+32y=8 (全式*4)
23y=23
y=1
代入3x+8y=2..........3x+8=2
3x=-6
x=-2



5(3r-1)+4(3+2s)=6
15r-5+12+8s=6
15r+8s=6+5-12
15r+8s=-1............. (1)

5(4-s)-6(2r+10)=12
20-5s-12r+60=12
5s+12r=60+20-12
5s+12r=68.........(2)

(1)*5.........75r+40s=-5............. (3)
(2)*8.........40s+96r=544
問題or答案應該錯,r=1,s=-2代入5(4-s)-6(2r+10)=5(4+2)-6(2+10)=30-72=-42 not 12



2x-5/3=x+3y/-2=1-y/3
4x-10=-3x-9y=2-2y(全式*6)
4x-10=-3x-9y
7x+9y=10............. (1)

4x-10=2-2y
2x-5=1-y
2x+y=6.........(2)
(2)*9........18x+9y=54............. (3)

(3)-(1).........11x=44
x=4
代入(2).......2*4+y=6
y=6-8

2007-01-24 02:34:29 補充：
(3)-(1).........11x=44x=4代入(2).......2*4 y=6y=6-8y=-2

第一題:
2X-y+4=12
2x-y=8
y=2x-8
25-3x+2(2x-8)=12
13=3x-4x+16
-3=-x
x=3
y=2(3)-8=-2
第二題
2(1-2x)-(3y-2)=9
2-4x=9+3y-2
2-4x=3y+7
-4x=3y+5
x=(3y+5)/(-4)
3(x-2)+2(4y+3)=2
3[(3y+5)/(-4)-2]+8y+6=2
-(3/4)(3y+5)-6+8y=-4
-(3/4)(3y+5)+8y=2
-3(3y+5)+32y=8
-9y-15+32y=8
23y=23
y=1
x=[3(1)+5]/-4=-2
第三條題目有錯,5(4-s)-6(2r+10)=12....(2)如果照答案r=1,s=-2,會得出5(4-s)-6(2r+10)=-32
所以答你唔到.
第四題
(2x-5)/3=(1-y)/3
2x-5=1-y
2x=6-y
x=(6-y)/2
{[(6-y)/2]+3y}/(-2)=(1-y)/3
3[(6-y)/2]+9y=2y-2
18-3y+18y=4y-4(呢步同上一步之間跳得遠少少,試下理解)
11y=-22
y=-2
2x-5=1-(-2)
2x=8
x=4