diketahui persamaan 2x - 3y = 20 dan x + 4y = -1. nilai 2xy adalah.... a. -28 b. 12 c. 20 d. 32

Kelas 8 Matematika
Bab SPLDV

x + 4y = -1
x = -4y - 1

2x - 3y = 20
2 (-4y - 1) - 3y = 20
-8y - 2 - 3y = 20
-11y = 20 + 2
y = 22/-11
y = -2

x = -4y - 1
x = -4 . (-2) - 1
x = 8 - 1
x = 7

2 . x . y = 2 . 7 . (-2)
2xy = -28