Finding an angle between two vectors

1. Nov 12, 2009

doublemint

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

Find the angle between the vectors u=[4 -4 -3] and v=[2 2 -3].

2. Relevant equations

theta = arccos(u . v)/(|u||v|)

3. The attempt at a solution

arccos[(8+(-8)+9)/(sqrt(41)*sqrt(17))]= 70.068 degrees. According to the online homework, it is wrong...and I and stumped.
Any help would be appreciated!

Thanks!

2. Nov 13, 2009

phyzmatix

3. Nov 13, 2009

doublemint

Well the thing is, it is a webwork assignment, so you can't really check the answer. And the question was not specfic for degrees or radians. Well, what counts is that I know I did it right. Thanks phyzmatix

4. Nov 13, 2009

phyzmatix

As a rule of thumb (well, this definitely holds for where I'm studying anyway) angles are ALWAYS in radians, unless specifically stated otherwise. It took me a while to get used to this also as we never did radians in school.