that is, the transform of the integral of f (t) is obtained by dividing the
transform of f (t) by jω and adding the result to the impulse term that
reflects the dc component F(0). Someone might ask, “How do we know
that when we take the Fourier transform for time integration, we should
integrate over the interval [−∞, t] and not [−∞,∞]?” When we integrate
over [−∞,∞], the result does not depend on time anymore, and
the Fourier transform of a constant is what we will eventually get. But
when we integrate over [−∞, t], we get the integral of the function from
the past to time t , so that the result depends on t and we can take the
Fourier transform of that.
If ω is replaced by 0 in Eq. (17.8),