Log_a 10, log_b 10, log_c 10 are in which progression, if a , b , c , are in gp?

if a,b,c are in  numbers are in gp then b²=ac, and if we take log on both sides then it will become  2logb=loga + logc. therefore loga, logb, logc are in AP. only possible when a,b,c are positive numbers.