The logarithm of a provided number b to the base 'a' is the exponent showing the power to which the base 'a' have to be raised to get the number b. This number is defined as log _{a }b. Therefore log a b = x ↔ ax = b, a > 0, a ≠1 and b>0. From the basic definition of the logarithm of the number b to the base 'a', we have an identity
That is called as Fundamental Logarithmic Identity.