Jawaban :

(1) C. -2

(2) C. 5

Penjelasan :

(1) eliminasi z pers 1 dan 2

x + y + z = 6

4x + 2y + z = 7

____________ -

-3x - y = -1 .... pers 4

eliminasi z pers 1 dan 3

x + y + z = 6

9x + 3y + z = 12

____________ -

-8x - 2y = -6 .... pers 5

eliminasi z pers 4 dan 5

-3x - y = -1 | ×2

-8x - 2y = -6 | ×1

____________

-6x - 2y = -2

-8x - 2y = -6

____________ -

2x = 4

x = 4 / 2 = 2

subs x ke pers 4

-3x - y = -1

-3(2) - y = -1

-6 - y = -1

-y = -1 + 6 = 5

y = -5

subs x dan y ke pers 1

x + y + z = 6

(2) + (-5) + z = 6

-3 + z = 6

z = 6 + 3 = 9

x - y - z = 2 - (-5) - 9 = 2 + 5 - 9 = -2

(2) 3x + 2y + z = 16 ... pers 2 => z = 16 - 3x - 2y ... pers 4

subs pers 4 ke pers 1

x - 3y + 2z = 1

x - 3y + 2(16 - 3x + 2y) = 1

x - 3y + 32 - 6x + 4y = 1

-5x + y = 1 - 32

-5x + y = -31

y = -31 + 5x .... pers 5

subs pers 4 ke pers 1

x - 2y + 3z = 8

x - 2y + 3(16 - 3x - 2y) = 8

x - 2y + 48 - 9x - 6y = 8

-8x - 8y = 8 - 48

-8x - 8y = -40 .... pers 6

subs pers 5 ke pers 6

-8x - 8y = -40

-8x - 8(-31 + 5x) = -40

-8x + 248 - 40x = -40

-48x = -40 - 248

-48x = -288

x = -288 / -48 = 6

subs x ke pers 5

y = -31 + 5x = -31 + 5(6) = -31 + 30 = -1

x + y = 6 + (-1) = 5