2log 3 = a dan 3 log 5 = b maka 4 long 15

Logaritma

⁴log 15
= ³log 15/³log 4
= ³log(5 ×3) / ³log (2²)
=( ³log 5 + ³log 3) / (2 . ³log 2)
= (b + 1) / (2 . 1/(²log3))
= (b + 1) / (2/a)
= (b + 1) × a/2
= (a(b +1))/2