Jika 3 log 2=x dan 2 log 5 = y maka 5 log 15 =....

³log 2 = x
²log 5 = y
Maka

³log 2 × ²log 5
= ³log 5
= xy

^5log 3
= 1/xy

^5 log 15
= ^5 log 5 × 3
= ^5 log 5 + ^5 log 3
= 1 + 1/xy
= (xy + 1) / xy