Ok,first of all ,I'm sorry for any further language barrier things,I study in a non-English speaking university,and I might do a mistake in translating some technical terminology. So,the problem is from mechanics of materials,buckling loads.This subject gives me nightmares as it is,I can barely understand what it is all about. 1. The problem statement, all variables and given/known data http://imageshack.us/photo/my-images/6/krisam.jpg http://imageshack.us/photo/my-images/6/krisam.jpg That is the problem basically.Trussel made of 3 beams,two rectangulars,one is round. First question is what is the minimal force to buckling. Second is,if we reverse the force (now it acts up instead of down),what is the minimal length of parameter a so that we can use Oiler formula. My attempt for solution : Non,I don't really know what they want from my life.Mostly,why they don't check if we can use Oiler formula in the first question,and why we have to check in the second? Thanks in advance.