Nilai x yang memenuhi sistem persamaan x + 2y -z = 3, 2x + y+ z =12, 3x – y + z = 11 adalah

X + 2y – z = 3 ……(i)
2x + y + z = 12 …(ii)
3x – y + z = 11 ….(iii)

x + 2y – z = 3 
2x + y + z = 12
——————– +
3x + 3y = 15 …….(iv)

2x + y + z = 12
3x – y + z = 11
——————– –
-x + 2y = 1 ……….(v)

3x + 3y = 15 I x1 I
-x + 2y = 1    I x3 I

3x + 3y = 15
-3x + 6y = 3
—————– +
9y = 18
y = 2

3x + 3y = 15
3x + 3(2) = 15
3x + 6 = 15
x = 3

x + 2y – z = 3
3 + 2(2) – z = 3
3 + 4 – z = 3
7 – z = 3
z = 4

HP = {(3, 2, 4)}

Nilai x = 3

X+2y-z=3
2x+y+z=12
3x-y+z=11

2x+y+z=12
3x-y+z=11
__________-
-x+2y = 1

x+2y-z=3     dikali -1
2x+y+z=12  dikali 1

-x-2y+z=-3
2x+y+z=12
_________-
-3x-3y = -15

-3x-3y = -15 dikali -2
-x+2y = 1     dikali 3

6x+6y = 30
-3x+6y = 3
_________-
9x      = 27
x        = 27/9
x        = 3