Diketahui sistem persamaan 3x + 7y = 1 dan 2x - 3y = 16. Nilai xy adalah...

3x+7y=1 kali 3 9x+21y=3
2x-3y=16 kali 7 14x-21y=112 +
23x=115
x=115/23 =5
3(5)+7y=1
15+7y=1
7y=-14
y= -2

xy=5.(-2)=-10

3x + 7y = 1 (1)
2x - 3y = 16 (2)

metode substitusi dari persamaan (1)
=>3x+7y=1
=>3x=-7y+1
=>x=(-7y+1)/3 (3)

x=(-7y+1)/3 maka
=>2x-3y=16
=>2[(-7y+1)/3]-3y=16
=>(-14y+2)/3-3y=16
=>(-14y+2-9y)/3=16
=>-23y+2=16×3
=>-23y=48-2
=>y=46/(-23)
=>y=-2

y=-2 maka
=>3x+7y=1
=>3x+7(-2)=1
=>3x+(-14)=1
=>3x=1+14
=>3x=15
=>x=15/3
=>x=5

xy=5×(-2)=(-10)