Jika x dan y adalah penyelesaian dari system persamaan 7x + 2y =19 dan 4x-3y =15, nilai dari 3x-2y adalah....

Mapel : Matematika
Kelas : VIII SMP
Bab : SPLDV

Pembahasan :
7x + 2y = 19 —» 6y = 57 - 21x
4x - 3y = 15 —» 6y = 8x - 30

Samakan...
6y = 6y
57 - 21x = 8x - 30
8x + 21x = 57 + 30
29x = 87
x = 3

Substitusi...
4x - 3y = 15
4(3) - 3y = 15
12 - 3y = 15
3y = 12 - 15
3y = -3
y = -1

Maka 3x - 2y = 3(3) - 2(-1) = 9 + 2 = 11

Bab Persamaan Linear
Matematika SMP Kelas VIII

7x + 2y = 19 → dikali 3 → 21x + 6x = 57
4x - 3y = 15 → dikali 2 →    8x - 6x = 30
                                        ---------------------- +
                                                 29x = 87
                                                     x = 3

4x - 3y = 15
4 . 3 - 3y = 15
3y = 12 - 15
y = -3/3
y = -1

3x - 2y = 3 . 3 - 2 . (-1)
3x - 2y = 9 + 2
3x - 2y = 11