Trigonometry Workbook For Dummies
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Logarithms are simply another way to write exponents. Exponential and logarithmic functions are inverses of each other. For solving and graphing logarithmic functions (logs), remember this inverse relationship and you'll be solving logs in no time! Here's the relationship in equation form (the double arrow means "if and only if"):

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Observe that x = by > 0.

Just as with exponential functions, the base can be any positive number except 1, including e. In fact, a base of e is so common in science and calculus that loge has its own special name: ln. Thus, logex = lnx.

Similarly, log10 is so commonly used that it's often just written as log (without the written base).

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Mary Jane Sterling taught algebra, business calculus, geometry, and finite mathematics at Bradley University in Peoria, Illinois, for more than 30 years. She is the author of several For Dummies books, including Algebra Workbook For Dummies, Algebra II For Dummies, and Algebra II Workbook For Dummies.

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