# Homework Help: Solving for Coordinate Angles in Statics Question

1. Sep 9, 2012

### RobertL

Edit: Nevermind, it has been resolved.

1. The problem statement, all variables and given/known data
I have been attempting to solve what seems like a relatively pedestrian statics questions, but for some reason my answer is being marked as incorrect. The problem is as follows:

Determine the magnitude and coordinate direction angles of the resultant force acting at A. Given that F_B = 640N and F_C = 450N.

http://imgur.com/U3dSG

2. Relevant equations

N/A (no specific equations needed)

3. The attempt at a solution

I solved for the value of the resultant vector without any trouble by assigning point A as the origin and adding the components of the two original vectors. This gave me a value of 998.05=R. The resultant vector had the equation of 626.667i+13.33j+776.667k.

My attempt at solving for the coordinate angles ended in failure:

For example:
alpha=cos^-1(626.667/998.05)=51.1 degrees, which is incorrect.

Any thoughts would be greatly appreciated.

Last edited: Sep 9, 2012