# Dot product, cross product

dextercioby
Homework Helper
HackaB said:
No, what you posted was an attempt to confuse the issue, and then show off some of your new found functional analysis jargon. You aren't helping anyone. You are just being a jackass.
I wasn't confusing any issue.I was interpreting a vague issue MY way.It is a mathematics problem and the way to do it correctly is less relevant.
As for not helping,i'm not helping you,maybe.Don't speak for someone else,unless you're paid to.

Jackass.

P.S.I think that MTV show really sukt. :yuck:

mathwonk
Homework Helper
jeanf: here is one way to think about problem 1, (although I know you understand it by now).

if two vectors have the same dot product with evrything, then in particular they are perpendicular to all the same vectors, so they must be parallel.

so one is a scalar times the other. to see what that scalar is just dot both of them with one of them.

i.e. if A = tB, then A.B = tB.B, so t = (A.B)/(B.B). but by hypothesis, A.B = B.B.

so t = 1.

so A = B.

arildno
Homework Helper
Gold Member
Dearly Missed
You are simply misunderstanding a vaguely stated exercise, Daniel.
If it had been specifically stated that a and c were fixed vectors (rather than tacitly assumed) we wouldn't have this conversation.

dextercioby
Homework Helper
I'm not misuderstanding anything.It was vague.It left room for interpretations.Mine was simply broader.

Daniel.

arildno
Homework Helper
Gold Member
Dearly Missed
When your interpretation is in conflict with the intended meaning then it is you who have misunderstood, even though it is the author's fault that he didn't state what he meant clearly and without ambiguity.

You guys have confused the living **** out of me, so I dont even know what the OP is going through. Besides set a good example. Lets be civilized.

dextercioby