There is a process called multiplication. To undo it, one uses division. There is a process called exponentiation. To undo it, one takes a logarithm. If a = b^c, then c = log_b(a) (log base b of a) e.g. 64 = 2^6, so 6 = log_2(64) natural logarithm (base e) is written ln logarithm base 10 is written log logarithm base 2 is written lg