# Geometry help

• Mar 2nd 2013, 12:53 PM
Minni04
Geometry help
Can someone please help me answer this? Can you upload the solutions to this past exam paper question please. I believe AB would essentially be u-w. So that is where i've started but still a bit puzzled here so solutions would be appreciated.

Thank you
• Mar 2nd 2013, 10:25 PM
a tutor
Re: Geometry help
$\displaystyle \mathbf{w}=\mathbf{u}+\vec{AB} \text { and } \vec{AB}.\mathbf{u}=0$ so what is $\displaystyle \mathbf{w.u}$?

I don't mind how many sites you post on

Geometry help - The Student Room

but it would avoid me wasting my time if you listed them.
• Mar 3rd 2013, 03:38 AM
Minni04
Re: Geometry help
Quote:

Originally Posted by a tutor
$\displaystyle \mathbf{w}=\mathbf{u}+\vec{AB} \text { and } \vec{AB}.\mathbf{u}=0$ so what is $\displaystyle \mathbf{w.u}$?

I don't mind how many sites you post on

Geometry help - The Student Room

but it would avoid me wasting my time if you listed them.

I did not know you would be on all sites. It was just to get lots of different insights from other people and because not everyone replies back on one forum so that's why I choose to post on a few.

Math Forum Discussions <--- no one has answered here

ok so with part a) i just need to do the dot product then? I don't quite get how I'm to do the dot product on that :/
• Mar 3rd 2013, 03:44 AM
a tutor
Re: Geometry help
OK. Now you know. :p Don't mind me. Bear in mind though that plenty of people help out on several forums.

$\displaystyle \mathbf{w.u}=(\mathbf{u}+\vec{AB}).\mathbf{u}$
• Mar 3rd 2013, 03:49 AM
Minni04
Re: Geometry help
Quote:

Originally Posted by a tutor
OK. Now you know. :p Don't mind me. Bear in mind though that plenty of people help out on several forums.

$\displaystyle \mathbf{w.u}=(\mathbf{u}+\vec{AB}).\mathbf{u}$

Oh my god yes duh!!! God, I'm so silly. I'm so used to a levels where we were usually doing the dot product with numbers because the vectors would be specified. Just a bit of algebra and that's the dot product.
So once I have the dot product of w&u, do i need to find the dot product of w&v from BC?