Professor Li is not easy, but he has reasonable expectations that he makes fairly clear. The lectures are not recorded, but he teaches directly from the book—I didn't attend many lectures and honestly think you're better off reading the textbook than attending Li's chaotic lectures. There are three quizzes during discussion sections: they are all basic and the lowest quiz score is dropped. The midterms and final are not easy by any means, with averages around 60% to 70% for all the tests, although there are two grading schemes (one with both midterms, one with only the best midterm). I never attended OH, but I heard Li is very receptive to students seeking help. At the end of the quarter, he adjusted the grade bounds down by almost 5%, so high grades are not impossible at all.

One of Professor Li's greatest strengths is his confidence in mathematics. He is rarely confused about his own work when showing examples, which grants a lot of clarity, even when his speech may be hard to understand at times. He goes quite fast during lectures, but this does benefit the pacing of the class, which is quite even and manageable. My personal favorite aspect of his class is the fair grading scheme and exams. He never does anything that is designed to make you fail or lower your grade. In other words, if you study the material and don't fall behind, Professor Li's class will be as wonderful as any.

I would suggest taking professor Li's class:
Class notes are quite clear and organized. He had all the materials prepared in draft paper that would be presented in his notes with oral explanations in the lectures.
Homework questions are carefully selected. You can review after class.
Professor was always willing to answer questions.
Many students complained that the exams were too hard and they were too different from quiz. It was true. However, you can find all the question types in previous homework. If you really want to have a solid foundation in calculus, the exams will motivates you to work hard and understand key points.

Although this class was challenging and took a lot of time and effort in my opinion, Professor Li did his best to help students understand the difficult concepts. As a new professor, I think he improved greatly throughout the quarter and got better at helping students. I would highly recommend going to his office hours. Although he does not usually give the final answers to homework problems, he will start them for you which is helpful. Even if you cannot attend office hours, he usually would be willing to stay after lectures and help students with homework problems or answer questions. Overall, going to him for help was the best for me since I did not have a good TA.
The homework for this class was assigned weekly every Monday and due on Sunday. Although there were not that many problems, many of them were challenging resulting in the homework taking a good amount of time. I definitely would recommend working on the sections of homework throughout the week and not waiting until Sunday to do the whole assignment. I usually would complete the problems for the most part during the week so I could ask questions during office hours on Friday. This helped me get 100 on all the homework assignments (although he does end up dropping your lowest homework score).
The quizzes were fairly easy. They typically consisted of 2-3 problems and were given in the last 15 minutes of discussion. He also dropped the lowest quiz score at the end of the quarter.
I found the exams in this class to be challenging. However, they did get easier and I think this had to do with the professor wanting to make the second midterm and final not as challenging as the first midterm. Li also offers 2 grading schemes in this class. Scheme 1 included: Homework: 15%, Quizzes: 10%, Midterm 1: 20%, Midterm 2: 20%, and Final: 35%. Scheme 2 included: Homework: 15%, Quizzes: 10%, Best midterm: 30%, and Final: 45%. At the end of the quarter, the professor goes in and calculates which scheme works in your favor. Having the second scheme as an option helped me out a lot since I did not do well on the first midterm.
Overall, although this class was challenging for someone who is not naturally good at calculus, I would say that Li was a good professor who wanted to help students.

Although Math 31B will always be a difficult class, I felt that Professor Li wanted his students to succeed, especially if they put in the effort. He is very helpful and will always try his best to answer a student's question. I would recommend attending his office hours, since I found that this helped answer any questions that I had on the homework/tests. For this class, there were 10 homework assignments, 3 quizzes, 2 midterms, and 1 final. I found the homework and quizzes a good way to boost your grade, while the midterms were the most difficult. But, he made a good portion of the final very similar to the practice final, which made the final a lot easier than both of the midterms. What helped my grade the most was having one of my midterms dropped so the final was weighted more heavily and I believe this was beneficial for many other students in the class. Overall, Professor Li was great and I definitely recommend him as a math professor.

ONE BIG PROBLEM: Lingfeng went to USC!!! Jokes aside, the class is decently easy and straightforward, and I felt like I pretty much mastered the concepts before the final. I was able to do this despite skipping most of this class. Difficulty ramps up significantly weeks 7-10 and into the final. Also, watch out for TRUE/FALSE questions on the tests, specifically the final, as they are worth way to much. I think I got pretty much every FRQ right on the final but 4 missed MC put my final exam grade down 20%. Other than that a fairly good course.

Easy class mid professor.

My experience with this class is that if you do the homework problems yourself and truly understand each one, you will be able to ace his exams. The midterms are not too bad, you just really need to be able to understand patterns and applying what you learn. The final was more like a huge unit test which did not focus on anything which was before midterm 2. There is a lot of partial credit given so even if you got the wrong answer on a problem, the amount of work you showed adds up and helps you gain some points. Overall, I think the class is extremely doable as long as you are willing to put in the effort.

He pulled out a tree branch in class to point at the board with. 10/10 recommend

Overall I liked 31B taught by Professor Li but I wouldn't say this is an easy class.
Good things about this class:
1. The professor is very helpful, he replies to your emails in a timely manner and is often willing to stay after class to answer your questions.
2. Workload is manageable, he gives less work during Thanksgiving break/midterm week.
3. Professor Li is genuinely a nice and chill person.
But there were things that went not so well:
1. Classes are not recorded or broadcasted.
2. Midterms were hard but the Professor was generous with partial credit.
3. The professor's teaching could've been clearer.