Originally Posted by

**pireskwared** I know I am going to have a problem like the following on an exam tomorrow. I have a few ideas but I am not getting far enough along with it. So, if someone could help me out it would be much appreciated. Here's the problem:

Two forces, one of 50lbs and the other of 30 lbs act on the same object. The magnitude of the resultant force is 70 lbs. Find the angle between the two forces.

Here are my thoughts. I know that three force vectors have the following relationship: F1 + F2 = F3. I know that the formula for deriving the cosine of the angle between two vectors is their dot product divided by the product of their magnitudes. And, I know that a vector can be described in terms of its magnitude and direction by v = ||v|| (cos@ + sin@) where @ = the angle to the horizontal axis. But I cannot figure out how to put it all together in order to solve the equation.

Thank you.