I'm completely stumped by the problem below because I haven't attended the lectures which used only Riemann integration and am not sure what the author is getting at.
Let $f\in C^1(\mathbb R)\cap L^1(\mathbb R)$. Let $\hat f$ be its Fourier transform. Define $$f_n(x)=\frac 1{2\pi}\int_{-n}^n\hat f(\omega)e^{i\omega x}d\omega$$
- Why is $f_n$ well defined?
- In what sense does $f_n$ converge to a function?
- Is there another sense in which $f_n$ necessarily converges to a function?
- Suppose $f\in C_c^\infty (\mathbb R)$. Prove the sequence converges uniformly.
- Where does $\hat f$ land assuming $f\in L^1(\mathbb R)\cap C^1 (\mathbb R)$?
- Umm... I think it converges pointwise almost everywhere since if $f$ is Lebesgue integrable the limit is just $\frac 1{2\pi}\int _\mathbb{R}\hat f(\omega)e^{i\omega x}d\omega$... What am I missing?
- ?
- I have no idea..