Logarithms Common Logarithms Integer Logarithms Negative Logarithms Log of a Product Log of a Quotient Log of an Exponential Natural Logarithms
Common Logarithms Key Point: The common logarithm of a number (N) is an exponent (x) where 10 x = N. The general equations is log 10 N = x where 10 x = N log = = 1000
Integer Logarithms Key Point: Only numbers that are powers of 10 will have logarithms that are whole numbers. log 10 = 1 log 100 = 2
Negative Logarithms Key Point: For any number between 1 and 0, the logarithm is a negative number. log 1 = 0 log 0.1 = ‑ 1
Log of a Product Key Point: Multiplication of numbers, using logarithms, is reduced to addition. The log of a product is the sum of the logs of the factors. log ab = log a + log b
Log of a Quotient Key Point: Division of numbers, using logarithms, is reduced to subtraction. The log of a quotient is the difference of the logs of the dividend and divisor. log a/b = log a - log b
Log of an Exponential Key Point: Raising a number to a power is a process of multiplication. log a x = x (log a)
Natural Logarithms Natural logarithms are exponents where e is the base. e log e N is usually written as ln N ln 10 = 2.30