I'm studying for a Master's degree in mathematics at the moment, after taking a break from studying for several years. As was then, my current area of interest is combinatorics and graph theory, which I suppose require a little less calculus and analysis than some other areas. Regardless, I still have to either read or perform algebraic manipulations sometimes, and I'm frequently at a loss in doing so. I'm talking about things like trigonometry, inequalities, limits, integrals, differential equations, etc., i.e. things usually covered in the first one or two years of college-level maths education. How do I bridge those gaps? Should I just re-learn those things as I go, or should I do the courses again?