1. The problem statement, all variables and given/known data A force F =( 6 i - 2 j ) N acts on a particle that under goes a displacement D r = ( 3 i + j )m. Find (a) the work done by the force on the particle and (b) the angle between F and D r . 2. Relevant equations I've found the work to be about 16N. My problem is finding the angle. The equation thebook gives is cos(inv)* (Products of vectors A and B) / (A)(i^2+j^2)*(B)(i^2+j^2) 3. The attempt at a solution I used cas(inv)*((VectorA * VectorB) / sqrt(6^2-2^2)(3^2+1^2)) Which came out to 26 degrees. The back of the book says 36.9 degrees for the answer. I don't think I'm missing anything. All your help is appreciated. Thank you.