I am given the following homework question to work with:
I am done with parts (a) and (b). But I cannot work on other parts because the concepts are not clear to me: what is exactly meant by "projection along a line" in part (c)? What is exactly the "closed convex hull" of a set in part (d), and why we can consider the functions of the form $\text{Re}[e^{i\theta} f(t)]$? I searched the terms on the internet but the results are not quite applicable to my level (I am taking an introductory second year complex analysis course).
Any hints to parts (c) and (d) would be appreciated a lot.