# Angle question

1. Mar 8, 2013

### kwal0203

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

Estimate to the nearest degree, the angles that a diagonal of a box with dimensions 10cm x 15cm x 25cm makes with the edges of the box.

2. Relevant equations

$cos\theta =\frac{u\cdot v}{\left \| u \right \|\left \| v \right \|}$

3. The attempt at a solution

For the angle between the diagonal vector and the edge with the 10cm side:

$u=(10,0,0)$
$v=(10,15,25)$

$cos\theta =\frac{(10,0,0)\cdot (10,15,25)}{\sqrt100\sqrt{100+225+625}}$
$cos\theta =\frac{100}{10\sqrt{950}}$

$cos\theta =\frac{10}{\sqrt{950}}$

Theta = ~71 degrees?

thanks, any help appreciated!

Last edited: Mar 8, 2013
2. Mar 8, 2013

### Vargo

Your denominator should be the product of the lengths of the two vectors. Vector u has length 10, right? Where's that? Vector v has length sqrt(950), why did you edit that to 100sqrt(850)?

3. Mar 8, 2013

### kwal0203

Oh yeah, I had it right the first time. But if I do that then I cant carry out the next step.. how would you proceed in this question?

4. Mar 8, 2013

### kwal0203

I edited it now, does it look right?

5. Mar 8, 2013

### Vargo

Yeah, that looks right.