# Vector Lengths

1. Oct 30, 2009

### Whiz

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

For u = (−1, 2, 1) and v = (3, 3, 6) find the ratio ||v|| / ||u||

2. Relevant equations

|| u || = (u^2 + u2^2 + ...un^2)^.5

3. The attempt at a solution

I found the || u || to be 6^(1/2) and || v || to be 54^(1/2)
Therefore the ratio should be 54^(1/2) divided by 6^(1/2), which calculates to 3. It turns out the answer is incorrect. Can anyone show me where I went wrong?

Thanks.

2. Oct 30, 2009

### LCKurtz

Nowhere.

3. Oct 31, 2009

### Staff: Mentor

I agree. The ratio is 3.

$$\frac{\sqrt{54}}{\sqrt{6}}~=~\frac{3\sqrt{6}}{\sqrt{6}}=~3$$

4. Oct 31, 2009

### Whiz

Okay thanks. I'll have to tell my instructor about it.

5. Oct 31, 2009

### Staff: Mentor

Before you do, make sure that the problem you posted here is exactly the same as in your book or wherever this problem came from.