where 
and
are replaced by
and 
respectively. This can be expressed in separate forms as follows
and
are replaced by
and respectively. This can be expressed in separate forms as follows
(11.22)
with
(11.23)
Equation (11.22) is called the Fourier transform of 
and equation (11.23) is called the inverse Fourier transform of 
. As an example, Figure 11.24 shows a square pulse defined as
