Capital is a book that explains the method of capitalism as a means of political control for the bourgeois of the proletariat or under-class. Thus, it is important to read this book with the idea that politics and economy are inseparable and that capitalism presents a means for the bourgeois to maintain power over the proletariat, primarily through the control of economic production and thus control of the state and people at a fundamental level.
Capital is also a fun book. Marx was very precise and thorough with his theories. A great read for anyone, but especially students of formal logic and political science.

Discrete Mathematics and Its Applications is a decent beginner discrete mathematics textbook that doubles as a beginner logic book (shockingly). The beginning pages of the textbook could be faster paced, though it is better a textbook be slow and elaborate than fast and incomprehensible. High-school level, it is a very easy book and could be completed in under a week.

An amazing and easy-to-follow precalculus book, both suited for high-schoolers and undergraduates who are looking to review or expand their knowledge of high-school mathematics. The proofs Lang wrote are simple and straightforward, and the book offers plenty of exercises (albeit, straightforward ones outside of some of the proofs). The book focuses heavily on beginner and informal exposure to the concepts of abstract algebra that pertain to classical non-modern algebra taught in most basic K-12 educations, which I'd assume was intentional given Lang's record.
Overall, I'd say it is one of if not the best early mathematics textbooks you can get your hands on. It's a fun read and is definitely worth the time it takes to complete.