The expansion is a special case of Taylor series around x=0, called the Maclaurin series. The derivation of the expansion of e^x can be found at: https://en.wikipedia.org/wiki/Taylor_series#Examples .

The expansion is a special case of Taylor series around x=0, called the Maclaurin series. The derivation of the expansion of e^x can be found at: https://en.wikipedia.org/wiki/Taylor_series#Examples .