急求4题方程计算（请简要写出计算过程）1.1/2(x+y)+1/3(x-y)=6(1)4(x+y)-5(x-y)=2(2)2.1/11(5x+3)+1/8(y-1)=2(1)x+y=-1(2)3.x+y+z=6(1)y:z=2:3(2)3x=z(3)4.2x+y+z=7(1)x+2y+z=8(2)x+y+2z=9(3)

Question

急求4题方程计算（请简要写出计算过程）
1.
1/2(x+y)+1/3(x-y)=6 (1)
4(x+y)-5(x-y)=2 (2)
2.
1/11(5x+3)+1/8(y-1)=2 (1)
x+y=-1 (2)
3.
x+y+z=6 (1)
y:z=2:3 (2)
3x=z (3)
4.
2x+y+z=7 (1)
x+2y+z=8 (2)
x+y+2z=9 (3)

Answer 1

1
(1)式×6得
3(x+y)+2(x-y)=36(3)
打开括号并合并同类项:5x+y=36(4)
(2)打开括号并合并同类项:-x+9y=2(5)
(4)+(5)×5得
46y=46;
则y=1;
代入(5)得x=5;
2.
(1)式×88得
8(5x+3)+11(y-1)=176;
打开括号并合并同类项:40x+11y=163(3);
(3)-11×(2)得
29x=174;
即x=6;
代入(2)得y= -7 ;
3.
(2)由比例公式可得
y=(2/3)z (4)
式(3)→x=z/3 (5)
(4)(5)代入得(1)
(2/3)z + (1/3)z +z=6;
×3后合并同类项得
6z=6×3
→z=3.
将z=3分别代入(4)(5)得
x=1 ;y=2;
4.
(2)-(3)得
y-z=-1 (4) ;
2×(3)-(1)得
y+3z=11 (5) ;
(5)-(4)得 4z=12;
z=3;
将z=3分别代入(4)得
y=2;
将y=2,z=3同时代入(2)得
x=1