AAaaaargh! I don't understand!! Aarggghh! 1. The problem statement, all variables and given/known data OK so I'm trying to understand the solution to a mechanics of materials problem that I'm working on. I understand the entire solution EXCEPT for 3 very tiny and BASIC lines of math which draw upon some BASIC trig property of which I must be unaware. 2. Relevant equations Attached (argh!.doc) is the segment of the problem that is driving me crazy. You will notice that under the picture of the problem are the words "Use member DEF as a free Body". You then see member DEF (in all its glory) and the forces acting on it. Now, the hideous lines that are driving me nuts are directly to the right of this diagram. They are the ones that say "Sigma F (unreadable symbol) = 0;" (sum of forces in some direction is zero) (3/5)Dy -(4/5)Dx = 0; Dy - 4/3Dx = 1200 lb. You can also see on the diagram that he somehow associates a 3-4-5 triangle to the reaction forces Dx and Dy. WTF?!!! I've taken statics before and I never saw anything like this. 3. The attempt at a solution Pleeeeease oh pleeease can one of you just explain this little section to me before I defenestrate myself (figuratively). Thanks. AAAARgh!!