MacLaurin series of Exponential function, 
The MacLaulin series (Taylor series at
) representation of a function
is
The derivatives of the exponential function
and their values at
are:
Note that the derivative of
is also
and
. We substitute this value of
in the above MacLaurin series:
We can also get the MacLaurin series of
by replacing
to
:
is used in Euler's Equation.