mohon bantuannya teman teman sekalian!!

Misalkan
y = log x
z = log y
maka sistem dapat ditulis

3y - z = 7 ......................(1)
-2y + 5z = -9 .................(2)

eliminasi 
15y - 5z = 35
-2y + 5z = -9
------------------- (+)
13y = 26
y = 2

subtitusi
-2y + 5z = -9
-2(2) + 5z = -9
5z = -9 + 4
5z = -5
z = -1

jadi
y = 2
log x = 2
x = 10²

y = -1
log y = -1
y = 1/10

jadi xy = 100/10
       xy = 10