Read a book by yourself. I've been looking for it for a long time and it's hard to find it. You can look at Wang Yuanming's special function, and it is easier to exchange two series of engineering mathematics. In addition, the key of mathematical physics method is method, which is the most deadly. Knowing the method can solve the problem, otherwise it will be embarrassing to recite the conclusion. I didn't find out until I graduated from college. Read a book by yourself. I've been looking for it for a long time and it's hard to find it. You can look at Wang Yuanming's special function, and it is easier to exchange two series of engineering mathematics. In addition, the key of mathematical physics method is method, which is the most deadly. Knowing the method can solve the problem, otherwise it will be embarrassing to recite the conclusion. I didn't find out until I graduated from college.