Logarithms De nition: y = log a x if and only if x = a y, where a > 0. In other words, logarithms are exponents. Remarks: log x always refers to log base 10, i.e., log x = log 10 x . ln x is called the natural logarithm and is used to represent log e x , where the irrational number e 2 : 71828. Therefore, ln x = y if and only if e y = x . Most ...