jika 2log 3 = x dan 3log 7 = y , maka 21log 54 =

2log 3 = log 3 / log 2 = x
3log 7 = log 7 / log 3 = y
21log 54 = log 54 / log 21
= log (27.2) //log (3.7)
= (log 27 + log 2) / (log 3 + log 7)
= (log 3^3+ log 2) / (log 3 + log 7)
= (3.log 3+log 2) / (log 3 + log 7). ganti bilangan pokok logariitma 3, maka
= (3.3log 3 + 3log 2) / (3log 3 + 3log 7)
= (3 + 1/x)/(1+ y)
= (3x +1)/x (1 + y)
= (3x + 1)/(x + xy)