If 3 numbers a,b,c are in G.P., then loga,logb,logc are in:
A.P
The three numbers a,b and c are in G.P., then
b2 = ac
Applying Log on both sides,
logb2=log(ac)
⇒2log10b = log10a+log10c (When three terms are in an A.P, Sum of the first and the third term is equal to twice the second term.)
Thus, loga,logb,logc are in AP