Question

Nilai (x-y) yang memenuhi sistem persamaan 5x+9y=12 dan 7/x+2 - 3/y+1 = 0

Answer 1

5x+9y=12 ...............(1)
7/x+2 - 3/y+1 = 0 [kali (x+2)(y+1)]
7(y+1)-3(x+2)= 0
-3x+7y= -1 ................(2)

Eliminasi (1) dan (2)

5x+9y=12 (kali 3) ..............(3)
-3x+7y= -1 (kali 5) .............(4)

Jumlahkan:
27y+35y= 31
62y= 31
y= 1/2 ⇒ Substitusi per (1) 
5x+9y=12 ⇔ 5x= 12-9/2 ⇔ x= 3/2

x-y= 3/2 - 1/2= 1 (D)