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431
ALGEBRA
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431

hence the series (1) is the xth power of the series (2); that is,


and this is true however great n may be. If, therefore, n be indefinitely increased, we have


The series is usually denoted by e; hence


Write cx for x, then


Now let e^c=a, so that c=\log_a; by substituting for c we obtain


This is the Exponential Theorem.

538. The series


which we have denoted by e, is very important, as it is the base to which logarithms are first calculated. Logarithms to this base are known as the Napierian system, so named after Napier, the inventor of logarithms. They are also