Question

Sistemas lineares

x + y + z = 207

- x + y = 15

- y + z = 12

Answer 1

$\begin{cases} & \text{x + y + z = 207 } \\ & \text{ - x + y = 15 } \to y = 15 + x \\ & \text{ - y + z = 12 } \end{cases} \\\\ -x + y = 15\\ -y + z = 12\\ Soma \\ -x + y -y + z = 15 + 12\\ z - x = 27\\ z = 27 + x\\ \boxed{z = 27 + x}\\\\ x + y + z = 207\\ x + 15 + x + 27 + x = 207\\ 3x + 42 = 207\\ 3x =165\\ \boxed{x = 55} \\\\ y = 15 + x\\ y = 15 + 55\\ \boxed{y = 70}\\\\ x + y + z = 207 55 + 70 + z = 207\\ z + 125 = 207\\ \boxed{z = 82}$

Answer 2

Olá
- x + y = 15   , y=15+x   x=y-15   
- y + z = 12  ,  z=12+y   -y=12-z, 
x + y + z = 207

(y-15) +y +(12+y)=207
y+y+Y+12-15=207
 3y=207+3
   y=210/3
  y=70
  
 y=15+x
70-15=x
  x=55
  
  Z=12+y
   Z=12+ 70
    z=82
     x+y+z=207
     55+70+82=207
     207=207
x=55,y=70,z=82