Question

x+y+z=4 2x+4-z=-5 x-2y+3z=9

Answer 1

x+y+z= 4
2x+y-z= -5
x-2y+3z= 9
-------------------

x+y+z= 4
(x= 4-y-z)

2x+y-z= -5
2(4-y-z)+y-z= -5
8-2y-2z+y-z= -5
8-y-3z= -5
-y= -5 -8 +3z (-1)
y= 5+8-3z
(y= 13-3z)

x-2y+3z= 9
1(4-y-z)-2.(13-3z)+3z= 9
4-1y-z-26+6z+3z= 9
4-1.(13-3z)-z-26+9z= 9
4-13+3z-z-26+9z= 9
-9+2z+9z-26= 9
-35+11z= 9
11z= 9+35
11z= 44
z= 44/11
[z= 4]

y= 13-3z
y= 13-3.4
y= 13-12
[y= 1]

x= 4-y-z
x= 4-1-4
x= 4-5
[x= -1 ]

Comprovando os valores:

x+y+z= 4 

-1+1+4= 4
4= 4

Answer 2

x + y + z = 4
2x + 4 - z = -5 --> 2x - z = -9
--> z = 2x + 9
x - 2y + 3z = 9

x + y + 2x + 9 = 4 --> 3x + y = -5
--> y = -3x - 5

x - 2(-3x - 5) - 2x - 9 = 9
x + 6x + 10 - 2x - 9 = 9
5x = 8
x = 1,6
y = -3(8/5) - 5 = -0,2
z = 2(8/5) + 9 = -5,8