Homework Help: Vector eqn problem

1. Oct 1, 2007

jean014

hello!

im new here and i just need a little help in solving this problem:
its a set of vector equation:

A = ai + bj + cK
B = -2i +j - 4K
C = i + 3j +2k

where A is an unknown vector. If

(AxB)+(AxC) = (5a + b)i + (3b-2)j + (-4c+1)k

i need to solve for a,b,c..

pls pls pls.. help! >.<

thanks

2. Oct 1, 2007

jean014

solving vector eqns using matrix inversion

hello!

im new here and i just need a little help in solving this problem:
its a set of vector equation:
1. The problem statement, all variables and given/known data

A = ai + bj + cK
B = -2i +j - 4K
C = i + 3j +2k

where A is an unknown vector. If

(AxB)+(AxC) = (5a + b)i + (3b-2)j + (-4c+1)k

i need to solve for a,b,c..

2. Relevant equations

matrix inversion by co-factor mtd or LU decomp..

3. The attempt at a solution

i dont even know where to begin!

pls pls pls help..

just on how to start .. or the algo ill finish the rest >.<

thnx!

3. Oct 1, 2007

D H

Staff Emeritus
To start you should calculate $A\times(B+C)$. You know B and C and have an expression for A.

4. Oct 1, 2007

HallsofIvy

Looks a lot like homework to me- so I'm going to move it to the "Homework- calculus and beyond" folder.

And, of course, you will have to make an effort yourself: What are AxB and AxC? That should be your first step. Then add those two and set them equal to the right hand side above. That will give you three equations to solve for a, b, c.

5. Oct 1, 2007

D H

Staff Emeritus
This is exactly the same problem as this thread. They should be merged. Jean, you are not supposed to post the same thing in multiple threads.

6. Oct 1, 2007

HallsofIvy

Thanks. I will.

(It was in "Engineering, Computer Science, and Technology"?? No wonder I didn't find it!)

Last edited by a moderator: Oct 1, 2007