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The natural logarithm of x is generally written as ln x, log e x, or sometimes, if the base e is implicit, simply log x. [2] [3] Parentheses are sometimes added for clarity, giving ln(x), log e (x), or log(x). This is done particularly when the argument to the logarithm is not a single symbol, so as to prevent ambiguity.
For example, from the differential equation definition, e x e −x = 1 when x = 0 and its derivative using the product rule is e x e −x − e x e −x = 0 for all x, so e x e −x = 1 for all x. From any of these definitions it can be shown that the exponential function obeys the basic exponentiation identity.
The identities of logarithms can be used to approximate large numbers. Note that log b (a) + log b (c) = log b (ac), where a, b, and c are arbitrary constants. Suppose that one wants to approximate the 44th Mersenne prime, 2 32,582,657 −1. To get the base-10 logarithm, we would multiply 32,582,657 by log 10 (2), getting 9,808,357.09543 ...
The logarithm of x to base b is denoted as log b (x), or without parentheses, log b x. When the base is clear from the context or is irrelevant it is sometimes written log x. The logarithm base 10 is called the decimal or common logarithm and is commonly used in science and engineering.
Inverse of logarithm integral. Define e x {\displaystyle e^{x}} to be the unique number y > 0 such that ∫ 1 y d t t = x . {\displaystyle \int _{1}^{y}{\frac {dt}{t}}=x.} That is, e x {\displaystyle e^{x}} is the inverse of the natural logarithm function x = ln ( y ) {\displaystyle x=\ln(y)} , which is defined by this integral.
The definition of e x as the exponential function allows defining b x for every positive real numbers b, in terms of exponential and logarithm function. Specifically, the fact that the natural logarithm ln(x) is the inverse of the exponential function e x means that one has = () = for every b > 0.
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The exponential function e x for real values of x may be defined in a few different equivalent ways (see Characterizations of the exponential function). Several of these methods may be directly extended to give definitions of e z for complex values of z simply by substituting z in place of x and using the complex algebraic operations. In ...