Home page for accesible maths Math 101 Chapter 2: Functions of a real variable

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2.27 Exponential series

Example

The exponential series

ex=n=0xnn!=1+x+x22!+x33!+e^{x}=\sum_{n=0}^{\infty}{{x^{n}}\over{n!}}=1+x+{{x^{2}}\over{2!}}+{{x^{3}}% \over{3!}}+\dots

converges for all real xx.

We can also consider

ez=n=0znn!=1+z+z22!+z33!+e^{z}=\sum_{n=0}^{\infty}{{z^{n}}\over{n!}}=1+z+{{z^{2}}\over{2!}}+{{z^{3}}% \over{3!}}+\dots

for any complex number zz.