Vector proofs :(

[jane1234]

Hi guys

I am completely lost in the world of vector proofs.

If it asks for proving things are perpendicular I know that the dot product must equal zero etc etc... but I never seem to be able to relate it to the shape! (Especially if given no specific numbers for vectors). I always end up saying a + b = c therefore a = c - b... and it never goes anywhere...

So does anyone have a nice, simple and formulaic way that they approach these proof questions?

[brightsky]

translate what is being asked into a vector equation or some sort, or at least an 'objective' in the form of vectors, and try to match up things that you find obvious, such as a = kb, a+b =? etc and work with them to see if you can get the required equation. also remember that for most eqns a max of 2 variables are introduced (thinking this way helps a lot with some questions). but other than that...i wouldn't say there's any other 'formulaic' way to approach vector proofs...they're built to be a pain, but a source of elation when you actually prove something with it. :p