Jika 2log3 = a dan 3log5 = b, maka 15log20 =

LogAritMa

²log 3 = a
³log 5 = b

15'log 20
= ³log 20 / ³log 15
= ³log (2² × 5) / ³log (3 × 5)
= (2 . ³log 2 + ³log 5) / (³log 3 + ³log 5)
= (2 . 1/a + b) / (1 + b)
= (2 + ab) / a(1 + b)
= (2 + ab)/(a + ab)