Hello everyone, I want to start by saying this is my first official visit to the forum, however I have been using the forum for several years to help me through my classes, and I owe a big thanks to all who are involved for getting me through some tough times! Now, on to my question..... I need some help on how to solve the equation for the angle of principle stress on a stress element. The equation is tan2∅=(shear stress/(stress in X-stress in Y)/2. I don't understand how to solve for ∅ in this equation, since I don't understand what to make of the tan2∅ term. How do I punch that into a calculator to solve this equation? I also don't understand how I'm suppose to get two seperate angles out of this equation (one for each of the principle stresses). Any help would be much obliged.