Hi,
I'm having some issues solving 7c. I already have AP, which I know is [6, 12, -18], but I can't work out how to get AB.
From the mark scheme, it says AP^(2) = 504, which I understand, but then it says 2AP^(2) = AB^(2) and this is the part I don't understand. How do I get 2AP^(2) = AB^(2).
Any help would be much appreciated. Apologies for the poor quality photo btw.