diketahui persamaan 2x - 5y + 12 = 0 dan 5x - 2y + 9 = 0 . Nilai 3x- 4y adalah

Kelas 8 Matematika
Bab Persamaan Garis

2x - 5y + 12 = 0 → dikali 5 → 10x - 25y + 60 = 0
5x - 2y + 9 = 0 → dikali 2 → 10x - 4y + 18 = 0

10x - 25y = -60
10x - 4y = -18
----------------------- -
-21y = -42
y = 2

2x - 5y + 12 = 0
2x - 5 . 2 + 12 = 0
2x = -2
x = -1

3x - 4y
= 3 . (-1) - 4 . 2
= -3 - 8
= -11

2x _ 5y + 12 = 0. x 5
5x _ 2y + 9 = 0. x 2

10x _ 25y + 60 = 0
10x _ 4y + 18 = 0
_______________ _
_ 21y + 42 = 0
y = _42/_21
y = 2

2x _ 5y + 12 = 0
2x _ (5 x 2) + 12 = 0
2x _ 10 + 12 =0
2x = 10 _12
2x = _ 2
x = _2/2
x = _1