I've been reading in my engineering textbooks and came across a frequent equation manipulation that involves multiplying/bringing the dx term of dy/dx to the other side of the equation, and then integrate both sides. I don't know what technique this is and I can't find it in my Stewart's Calculus either. Please help me find out what this is and how I can read about it more. I've heard that the individual dy and dx terms are called infinitesimals but when I googled infinitesimal calculus, the results all went way over my head (wtf is hyperreal?) I really need your help because I'm starting to get lost on the math on my engineering classes. Thank you. Edit: okay I've just done some googling and it turned out to be a simple differential equation problem. Since I have not taken any differential equation yet, what is a good way to quickly gain ground on this topic so that it could be useful for other classes while not getting bogged down so much that it's like another class of its own.