Question

x-y+3z=5 -x+2y-z=5
x-5y+4z=-17
O valor de x+y+z é igual a ? ​

Answer 1

Resposta:

 x-y+3z=5   ==> x-y+3*(-x+2y-5)=5 ==>-2x+5y-20=0 (i)

-x+2y-z=5    ==>z=-x+2y-5 (ii)

 x-5y+4z=-17 ==> x-5y+4(-x+2y-5 )=-17 ==>-3x+3y-3=0  (iii)

3(i) -2(iii)

-6x+15y-60+6x-6y+6=0

9y-54=0

y=54/9 =6

Usando (i) ==>-2x+5*6-20 =0 ==>x=-10/(-2)=5

Usando (ii) ==> z=-5+2*6-5 = 2

x=5

y=6

z=2

x+y+z =5+6+2 = 13