跪求大师帮我做几道方程组得题,解方程组1.7x+3y=762x-9y=22.17x+25y=6725x+17y=593.2x-y=-43y-2z=6z+x=-34.x+y-2z=52x+2y-z=73x-y-6z=7解关于x,y,z的方程组1.x+y=-4x+z=9y+z=1最好有过成

Question

跪求大师帮我做几道方程组得题,
解方程组
1.7x+3y=76 2x-9y=2
2.17x+25y=67 25x+17y=59
3.2x-y=-4 3y-2z=6 z+x=-3
4.x+y-2z=5 2x+2y-z=7 3x-y-6z=7
解关于x,y,z的方程组
1.x+y=-4 x+z=9 y+z=1
最好有过成

Answer 1

7x+3y=76 (1)
2x-9y=2 (2)
(1)*3+(2)
21x+2x=228+2
23x=230
x=10,代入(1)
70+3y=76
y=2
17x+25y=67 (1)
25x+17y=59 (2)
相加
42x+42y=126
x+y=3
25x+25y=75 (3)
(3)-(1)
8x=8
x=1
(3)-(2)
8y=16
y=2
2x-y=-4 (1)
3y-2z=6 (2)
z+x=-3 (3)
(2)+(3)*2
3y+2x=0 (4)
(4)-(1)
4y=4
y=1
z=(3y-6)/2=-3/2
x=-3-z=-3/2
x+y-2z=5 (1)
2x+2y-z=7 (2)
3x-y-6z=7 (3)
(1)+(2)
4x-8z=12
x-2z=3 (4)
(1)*2-(2)
-4z+z=10-7
z=-1
x=3+2z=1
y=5-x+2z=2
x+y=-4 (1)
x+z=9 (2)
y+z=1 (3)
相加
2(x+y+z)=-4+9+1=6
x+y+z=3 (4)
(4)-(1),z=7
(4)-(2),y=-6
(4)-(3),x=2