Question

Calcule o valor de 2z-y no sistema :? x+y = 4 2x-z= -2 y+z = 7

Answer 1

Oi

x + y = 4       (I)
2x - z = -2     (II)
y + z = 7       (III)

de (II) vem 
z = 2x + 2

de (I) e (III) vem
x + y = 4
y + 2x = 5

2x - x = 1

x = 1
y = 3
z = 4 

valor de 2z - y = 8 - 3 = 5