The document discusses methods for solving different types of first-order differential equations (DEs). It explains that separable DEs can be solved by separating the variables, while linear DEs require using an integrating factor to solve for the general solution. Non-separable DEs cannot be solved by separating variables alone. Examples are provided to demonstrate solving linear first-order DEs using an integrating factor to get the general solution and imposing initial/boundary conditions to get the particular solution.