1.3(x+y)-4(x-y)=4 x+y/2 + x-y/6 =6 2.x+2y+3z=7 2x+y+z=7 3x+y+2z=11 3.x:y:z=1:2:7 2x-y+3z=214.4x-3y=1 x+2y-z=5 3x-y+2z=2
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1.3(x+y)-4(x-y)=4 x+y/2 + x-y/6 =6 2.x+2y+3z=7 2x+y+z=7 3x+y+2z=11 3.x:y:z=1:2:7 2x-y+3z=214.4x-3y=1 x+2y-z=5 3x-y+2z=2
1.3(x+y)-4(x-y)=4 x+y/2 + x-y/6 =6 2.x+2y+3z=7 2x+y+z=7 3x+y+2z=11 3.x:y:z=1:2:7 2x-y+3z=21
4.4x-3y=1 x+2y-z=5 3x-y+2z=2
1.3(x+y)-4(x-y)=4 x+y/2 + x-y/6 =6 2.x+2y+3z=7 2x+y+z=7 3x+y+2z=11 3.x:y:z=1:2:7 2x-y+3z=214.4x-3y=1 x+2y-z=5 3x-y+2z=2
1:1.3(x+y)-4(x-y)=4,(1)
x+y/2 + x-y/6 =1 (2)
由(1),得:x=7y-4,代入(2),得
14y-y/3=9,y=27/41,x=25/41
2.5x+4y+z=0,(1)
3x+y-4z=11,(2)
x+y+z=-2 (3)
4(1)+(2):
23x+17y=11 (4)
(1)-(3):
4x+3y=2 (5)
3(4)-17(5):x=-1
由(5),y=2
由(3),z=-3
1: x＝122/5 y＝26/15
2: x＝11/4 y＝1/4 z＝5/4
3: x＝1 y＝2 z＝7
4: x＝13/9 y＝43/27 z＝－10/27
1.3(x+y)-4(x-y)=4 ......(1)
x+y/2 + x-y/6 =6 ......(2)
又（1）得7y-x=4......得x=7y-4
代人（2)式得(4y-2）+（3y-2）/3=6
得y=26/15,x=122/5
2.x+2y+3z=7.....(1)
2x+y+z=7......(2)
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1.3(x+y)-4(x-y)=4 ......(1)
x+y/2 + x-y/6 =6 ......(2)
又（1）得7y-x=4......得x=7y-4
代人（2)式得(4y-2）+（3y-2）/3=6
得y=26/15,x=122/5
2.x+2y+3z=7.....(1)
2x+y+z=7......(2)
3x+y+2z=11 ......(3)
由（3）-（2）得x+z=4即z=4-x......（4）
由(1)-2乘以(2)得z-3x=-7即z=3x-7.....(5)
得x=11/4 代入（4）式得z=5/4所以 y＝1/4
3. x:y:z=1:2:7 （1）
2x-y+3z=21 （2）
由（1）得y=2x,z=7x代入（2）式
得x=1, y＝2 z＝7
4.4x-3y=1.......(1)
x+2y-z=5....... (2)
3x-y+2z=2......(3)
由2乘以（2）式+（3）式得5x+3y=12.....(4)
由（1）+（4）式得x=13/9,
依次代入得 y＝43/27 z＝－10/27
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第一题
3(X+Y)-4(x-Y）=4 （1） 3X+3Y-4x+4Y=4 -x+7y=4 -4x+28Y=16
X+Y/2+X-y/6=6 (2) 3x+3Y+x-Y=36 4x+2Y=36 4x+2Y=36
两个等式相加得出 Y=26/15 X=122/15
第二题