Is it possible to stand backwards on a flight of stairs?

yes

Explanation:

if your destination is on the top floor, but you are facing towards the bottom floor, you are facing the wrong way. It's all relative. Honestly, I hate this question, because then it turns into, is it possible to go backwards anywhere. Backwards and forwards, right and left, it's all relative to which way you are facing and where you want to go. If something is on the left and you turn 180 degrees, then that thing is on the right. If you are going forward towards your house and you turn around, you are now going backwards, relative to your house. But if your perspective is relative to that tree in the opposite direction of your house, you are now facing the right way. See, it's all relative to where you are going.

pythagoras' theorem

square root (-5^2+9^2)

square root (25+81)

square root (106)

angle is tan^-1(9/5)

neg x, pos y