Yang nmr 21 sama nmor 22

21.
2x -y + 3z = 2
2x- y – z = 2
…………………(-)
4z = 0
z = 0

x+ y + z = 1 –> x + y = 1
2x-y -z = 2 —> 2x-y = 2
———————————-(+)
3x = 3
x = 1

x + y = 1
y = 1 – x 
y = 1-1
y = 0

x,y,z = (1,0,0)

22.
x + y + z = 2
x – y – z = 0
—————(+)
2x = 2
x = 1

x + y + z = 2
2x-y+ z = -1
—————-(+)
3x + 2z = 1
3(1) + 2z = 1
2z = 1-3 = -2
z = -1

x+ y + z = 2
1 + y – 1 = 2
y = 2

x,y,z = 1,2,-1