Question

{x-y=0
{x+y+z=4
{x+2y+3z=9

Answer 1

Z pierwszego

x=y

czyli

{y+y+z=4
{y+2y+3z=9

2y+z=4
3y+3z=9 //3

2y+z=4
y+z=3
odejmujemy stronami

y=1
z=2
x=1

Answer 2

{x-y=0
{x+y+z=4
{x+2y+3z=9

{x = y
podstawiamy
{x + x + z = 4
{x + 2x + 3z = 9

{2x + z = 4
{3x + 3z = 9 /:3

{x + z = 3
{2x + z = 4

{x = 3 - z
{2 (3 - z) + z = 4

6 - 2z + z = 4
-z = 4 - 6
-z = -2
z = 2

x = 3 - 2
x = 1

{x = 1
{y = 1
{z = 2