Need help for vector product

For discussing Olympiad level Geometry Problems
sourav das
Posts:461
Joined:Wed Dec 15, 2010 10:05 am
Location:Dhaka
Contact:
Need help for vector product

Unread post by sourav das » Sat May 21, 2011 6:44 pm

I really need some help about vector product. (Specially cross multiplication) And i want an answer with explanation of the value of \[\vec{a}\times \vec{b}= ?\] where \[\vec{a}= \frac{2\vec{x}+\vec{y}}{3}\]
And \[\vec{b}= \frac{2\vec{p}+\vec{q}}{3}\]
You spin my head right round right round,
When you go down, when you go down down......
(-$from$ "$THE$ $UGLY$ $TRUTH$" )

User avatar
Moon
Site Admin
Posts:751
Joined:Tue Nov 02, 2010 7:52 pm
Location:Dhaka, Bangladesh
Contact:

Re: Need help for vector product

Unread post by Moon » Thu May 26, 2011 7:16 pm

Physically the cross product means the area of a parallelogram with two adjacent sides $\vec{a},\vec{b}$.
$\dfrac{2\vec{x}+\vec{y}}{3}$ means the position vector of a point which has $\vec{x}$ and $\vec{y}$ as the position vector of the terminal points (and the segment between those two terminal points is divided into ratio $2:1$ by the first point).

I don't think that we can specifically conclude anything special from just these equations. We need more info about what we want to prove. :)
"Inspiration is needed in geometry, just as much as in poetry." -- Aleksandr Pushkin

Please install LaTeX fonts in your PC for better looking equations,
learn how to write equations, and don't forget to read Forum Guide and Rules.

Mehfuj Zahir
Posts:78
Joined:Thu Jan 20, 2011 10:46 am

Re: Need help for vector product

Unread post by Mehfuj Zahir » Fri May 27, 2011 4:57 am

In 3 d space to calculate the vector product you must know about three axis .Here you dont mentioned about axis and its not possible to give answer according to given condition

tanvirab
Posts:446
Joined:Tue Dec 07, 2010 2:08 am
Location:Pasadena, California, U.S.A.

Re: Need help for vector product

Unread post by tanvirab » Fri May 27, 2011 7:24 am

from the information you have given, the only thing that can be found is:

$\vec{a}\times \vec{b}= \frac{4}{9} \vec{x} \times \vec{p} + \frac{2}{9} \vec{x} \times \vec{q} + \frac{2}{9} \vec{y} \times \vec{p} + \frac{1}{9} \vec{y} \times \vec{q}$

sourav das
Posts:461
Joined:Wed Dec 15, 2010 10:05 am
Location:Dhaka
Contact:

Re: Need help for vector product

Unread post by sourav das » Fri May 27, 2011 10:38 am

Oh! I forget to mention, it is 2d space. (Actually i got it when i was solving a Geometry Unbound problem)
You spin my head right round right round,
When you go down, when you go down down......
(-$from$ "$THE$ $UGLY$ $TRUTH$" )

Post Reply