Hitunglah nilai 2x - 3y joka diketahui 4x + y = 9 dan x + 4y = 6

Bab Persamaan Linear
Matematika SMP Kelas VIII

4x + y = 9
y = -4x + 9

x + 4y = 6
x + 4(-4x + 9) = 6
x - 16x + 36 = 6
-15x = 6 - 36
x = -30 : (-15)
x = 2

4x + y = 9
4 . 2 + y = 9
y = 9 - 8
y = 1

2x - 3y = 2 .2 - 3 . 1
            = 4 - 3
            = 1