计算log根号48分之7加log12减二分之一log21

lg(7/48)^(1/2)+lg12-(1/2)lg21
=lg(7/48)^(1/2)+lg[12^2]^1/2-(1/2)lg21
=(1/2)lg(7/48)+(1/2)lg144-(1/2)lg21
=(1/2)lg[(7/48)*144/21]
=(1/2)lg1=0