For the a part, im a bit iffy about my way in doing part (IV) yet but il keep trying. cbb to b) but im sure if you manipulate around a bit you'l get there.
im sure you can show that formula
ii) it seems a gift IMO. sub in (ae,0) and you'l get it
iii) i used y2 - y1 / x2 - x1 and you notice how...