I've got a TI-89 Titanium I've taking a class in Mechanical Design and my professor informs me that we need to be able to solve the equation (equation 3-15) shown in the attachment. I've been trying to find a way to program it into my calculator, but haven't had any real success. The purpose of the program is to solve for sigma I tried writing a program with ProgramEditor. I followed the outline given at: https://epsstore.ti.com/OA_HTML/csksxvm.jsp?nSetId=91276 But when I attempt to use the equation in HOME it asks me for sigma, which is what I want to solve for. Any suggestions on what I could do? Help is always appreciated.