# Vectors (ii)

• Apr 30th 2007, 12:15 PM
r_maths
Vectors (ii)
http://img252.imageshack.us/img252/8013/vectorub0.png

Can someone tell me how to arrive to the answer. 1/2(u + 3v)

Thanks
• Apr 30th 2007, 12:46 PM
topsquark
Quote:

Originally Posted by r_maths
http://img252.imageshack.us/img252/8013/vectorub0.png

Can someone tell me how to arrive to the answer. 1/2(u + 3v)

Thanks

From the diagram it looks to me like BD = v... Something doesn't "add up" (if you don't mind the pun.)

-Dan
• Apr 30th 2007, 01:41 PM
r_maths
Ah, sorry.

BC not BD. :o

(awful pun lol)
• Apr 30th 2007, 04:10 PM
ThePerfectHacker
Quote:

Originally Posted by topsquark
From the diagram it looks to me like BD = v... Something doesn't "add up" (if you don't mind the pun.)

I love that pun! Much funnier than all puns I make.
• May 1st 2007, 06:15 AM
r_maths
Am I right to say the arrows play a part into getting the answer?
• May 1st 2007, 10:24 AM
ThePerfectHacker
Quote:

Originally Posted by r_maths
Am I right to say the arrows play a part into getting the answer?

Yes. If you have the arrows backwards then you different answers when you find the vector sum.
• May 1st 2007, 10:34 AM
earboth
Quote:

Originally Posted by r_maths
http://img252.imageshack.us/img252/8013/vectorub0.png

Can someone tell me how to arrive to the answer. 1/2(u + 3v)

Thanks

Hello,

I've tried to get a solution of this problem and I failed very successfully :(

Could it be that the proportion reads:

AD : DC = 2 : 1 (?)

If so, the solution is:

1. AD = u + v

3. BC = -u + AD + DC

BC = -u + u+v + (1/2)*(u+v) = v + (1/2)*u + (1/2)*v = (1/2)*(u + 3v)
• May 1st 2007, 10:50 AM
r_maths
My apologies, it is AD : DC
-
Two mistakes in just copying out one question :(

Thanks alot by the way.
• May 2nd 2007, 12:43 AM
earboth
Quote:

Originally Posted by r_maths
...it is AC : DC
...

Hi,

now it's me who is really confused - because:

AC = AD + DC. Therefore:

AC/DC = 2 ==> AC = 2*DC ==> AD + DC = 2*DC ==> AD = DC

From my previous post you know that

BC = -u + AD + DC

BC = -u + u+v + u+v = u + 2v