Ok, I got stuck in this question.
I Dont know if I forgot this method or it is something new to me.

picture in comment section. I had problems specifically with the expanding part

Question

Ok, I got stuck in this question.
I Dont know if I forgot this method or it is something new to me.

picture in comment section. I had problems specifically with the expanding part

archtangent · Answer

attachment

archtangent · Answer

@ganeshie8 what do you think sir?

qwertty123 · Answer

Hey sorry I can't help you! I would love to if I new how! :D Good luck on this!

empty · Answer

So those $a_x$ thingies are the unit vectors and give the direction of each component. When they say expand, what they mean is find the length of that vector, which is what these lines around the stuff mean: $| stuff|$ 

What's the length? Just the pythagorean theorem really: 
$$\sqrt{x^2+y^2+z^2 }$$ where x, y, and z are the components multiplying those unit vectors I descried earlier. 

A small note is instead of taking the square root, they just squared both sides of the equation so that's why that 10 became 100 on the right and you don't see the square root with all the garbage that got expanded... Phew...

archtangent · Answer

I am so ashamed, thanks for bringing me back. I noticed the squaring of both sides but I was too boggled by the middle term 8B then realized it is (6-2/3)^2

phi · Answer

typo: (6-2B/3)^2

phi · Answer

they also were not very straight-forward when writing down B-A
i.e. they flipped signs around (it does not matter for the answer, but it makes it that much harder to follow what they are doing)