(It was funny when I got your post back: "Failure has replied to your post"

)

I followed it through and it was much easier than using coordinates.

I could write it out in terms of coordinates, but I don't think it would get any simpler.

I'm also sorry for springing this on you, but I hoped this would help me solve part ii) of the question. Unfortunately, i'm still lost:

So I know that:

and:

Therefore:

(putting the first one into the second one, for some vector

).

Expanding this out gives:

If it didn't say "hence calculate...", I probably would have left it there.

At this point I thought I could group the terms together to get

appearing somewhere (or at least

). A big obstacle is that

doesn't really pop up. I tried seeing if there was a link between

and

, but writing them out doesn't produce anything.