Please bantuin no 9 dan 10 Thanks....

9) 2x - y + z = 7
- x - 2y + z = 6
---------------------(-)
3x + y = 1 ... pers 1

- x - 2y + z = 6
4x - 2y - z = 5
---------------------(+)
3x - 4y = 11 ... pers 2

pers 1 & 2
3x + y = 1
3x - 4y = 11
-----------------(-)
5y = - 10
y = - 2

subtitusi
3x + y = 1
3x - 2 = 1
3x = 1 + 2
3x = 3
x = 1

subtitusi
2x - y + z = 7
2(1) - (-2) + z = 7
2 + 2 + z = 7
4 + z = 7
z = 7 - 4
z = 3

nilai x² + y² + z²
= ( 1 )² + ( - 2)² + (3)²
= 1 + 4 + 9
= 14 ( C )



10) x + y + 2z = 1
4x + 2y + z = 4 |×2
maka
x + y + 2z = 1
8x + 4y + 2z = 8
------------------------(-)
- 7x - 3y = - 7 ... pers 1

x + y + 2z = 1
9x + 3y + z = 17 |×2
maka
x + y + 2z = 1
18x + 6y + 2z = 34
----------------------------(-)
- 17x - 5y = - 33 ... pers 2

- 7x - 3y = - 7 |×5
- 17x - 5y = - 33 |×3
maka
- 35x - 15y = - 35
- 51x - 15y = - 99
-------------------------(-)
16x = 64
x = 4

subtitusi
- 7x - 3y = - 7
- 7(4) - 3y = - 7
- 28 - 3y = - 7
- 3y = - 7 + 28
- 3y = 21
y = - 7

subtitusi
x + y + 2z = 1
4 - 7 + 2z = 1
- 3 + 2z = 1
2z = 1 + 3
2z = 4
z = 2

nilai x + y + z
= 4 + ( - 7 ) + 2
= - 1 ( B )