tentukan 3xy! 5x+y=15 3y-x=3

5x+y=15
3y-x=3
..
5x + y = 15 ..... (×3)
- x + 3y = 3
..
15x + 3y = 45
x + 3y = 3
------------------- --
14 x = 42
x = 42/14
x = 3

5x + y = 15
5(3) + y = 15
15 + y = 15
y = 15 - 15
y = 0

3xy = 3(3)(0) = 0

Jadi nilai 3xy adalah 0