Answer :

In mathematics, the logarithm of a number is the exponent to which another fixed value, the base, must be raised to produce that number. 

For example
log(base e) *1

=> e^0 =1

thus 
log(base e) * 1= 0 

in general, if a raise to the power n equal to x, we write it as logx to the basea =n where x and a are postive numbers and not= 1

example
in eponential form 4 raise to power 2 =16
in logarithamic form log 16 to the base 4 =2