3 log 81 - 2 log 20 - 2 log 2/5 + 5 log 125 =

= 3 log 3^4 - ( 2 log 4 + 2 log 5) - ( 2 log 2 - 2 log 5 ) + 5 log 5^3
= 4 - ( 2 + 2 log 5 ) - ( 1 - 2 log 5 ) + 3
= 7 - 2 - 2 log 5 - 1 + 2 log 5
= 4
Note :
^ = pangkat

Sifat logaritma :
a log a^n = n
a log a = 1
a log b/c = a log b - a log c
a log b.c = a log b + a log c

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