3x+y+14=0 dan 2x-2y+4=0.nilai4x-5y

[tex]3x+y+14=0 \\ 2x-2y+4=0 \\kurangkan \\ x + 3y + 10 = 0 \\kurangkan \\x - 5y - 6 = 0 \\ kurangkan \\8y + 16 = 0 \\ y = - \frac{16}{8} = - 2 \\ \\ 3x+y+14=0 \\ 3x + ( - 2) + 14 = 0 \\ 3x + 12 = 0 \\ x = - \frac{12}{ 3 } = - 4\\ \\ 4x-5y = 4( - 4) - 5( - 2) \\ 4x - 5y = - 16 + 10 \\ 4x - 5y =-6[/tex]

3x + y + 14 = 0
3x + y = -14 (kalikan setiap ruas dengan 2)
6x + 2y = -28 ........................(1)

2x - 2y + 4 = 0
2x - 2y = -4 ...........................(2)

dari (1) dan (2)
6x + 2y = -28
2x - 2y = -4
-------------------- (+)
8x = -32
x = -4

subtitusi x = -4 ke pers (2)
2x - 2y = -4
2(-4) - 2y = -4
2y = -8 + 4
2y = -4
y = -2

jadi 
4x - 5y 
= 4(-4) - 5(-2)
= -16 + 10
= -6