# Homework Help: What then is in unit-vector notation

1. Mar 29, 2007

### norcal

1. The problem statement, all variables and given/known data

In the product F = qv x B , take q = 4,
v = 2.0i + 4.0j + 6.0k and F= 136i -176j + 72k.
What then is in unit-vector notation if Bx = By?

2. Relevant equations

136i-176j+72k = 8i+16j+24k X Bxi+Byj+Bzk

3. The attempt at a solution

I am stuck with the above equation. How do I solve for Bxi, Byj and Bzk?

136i-176j+72k=8i+16j+24k X Bxi+Byj+Bzk
So If I find the determinant from the right hand side it's:
136i-176j+72k=((16)(Bz)-(By)(24))i+((24)(Bx)-(Bz)(8))j+((8)(By)-(16)(Bx))k
136i-176j+72k=(16Bz-24By)i+(24Bx-8Bz)j+(8By-16Bx)k

Now what do I do???

2. Mar 29, 2007

### denverdoc

If i were you i'd post this on one of the math forums. This isn't likely to get much response here.

3. Mar 29, 2007

### Andrew Mason

Since i, j and k are mutually orthogonal unit vectors, then 16Bzi-24Bxi = 136i. You also know that Bx = By, so 8By-16Bx = 72 gives you the value for Bx and By. From that you can figure out Bz.

AM