The probability of learning calculus is not difficult at best (some of them may not need to learn yet), but it is different if you are prepared to learn mathematics, not to mention that if your original major is liberal arts mathematics, you will have to work harder, but the starting point of mathematics in American universities is lower than that in high schools in China, so don't worry too much about giving the simplest example. The first thing you learn at first is often the derivative we recite.

1. Statistical probability, integral, differential, complex variable, linearity and various analysis should be compulsory courses for mathematics majors, so it is good to learn them well. Elective courses are all about cultivating hobbies, such as learning a second foreign language.

It doesn't seem so easy to change majors in America. I just heard that it should still be possible to change majors.

3. books? Is it to preview college mathematics or consolidate high school mathematics? I don't know. In fact, there is basically no need to consolidate preview. High school knowledge is the cornerstone of all mathematics subjects. Consolidate and understand high school mathematics knowledge, and be not afraid of anything (including theoretical physics).