I'm just starting my first semester of Calculus and am wondering why there are so many versions of this book. I've been told that the single variable version will only get me through the first two semesters and the full book (the one just titled Thomas' Calculus) would get me through calc 1-3. But then there's multivariable and early transcendents. What are those? Is the full book just single variable and another book combined?