10: Logarithms
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”You have no idea, how much poetry there is in the calculation of a table of logarithms!” - Carl Friedrich Gauss
Chapter ten is dedicated to a fan favorite: the logarithm. This feisty function is defined entirely as an inverse, and yet it is incredibly powerful in calculus.
We give the official definition of a logarithmic function as the inverse of an exponential function. This immediately tells us the graph of any member of the log family, as well as its domain and range. We also inherit properties of logarithms based on properties we know of exponential functions. Since the exponential functions are continuous, so are the logarithmic functions on their entire domain. Taking limits involving logs is usually pretty painless.
One powerful application of the logarithm is that we can use it to solve exponential equations (which are equations with variables in the exponent). Mastering the properties of the logarithm often makes solving these equations easier. There are even real life examples of exponential growth and decay, or temperature change models where using logarithms is essential to find a solution.
Once again our inverse derivative formula comes in handy to help us learn the derivative of the logarithmic functions, as well as how to use them in combination with our previously memorized derivative shortcuts. In fact the properties of the logarithm can be used in a special process called logarithmic differentiation to help us take derivatives of some even more difficult and extreme functions.