I bought it on the online class platform. The online class platform I am using is Tencent Classroom, and there are many other online class platforms. Li Yang's intensive lecture on Advanced Algebra was purchased on the online course platform. Tencent Classroom is a professional online education platform launched by Tencent, which has gathered a large number of high-quality educational institutions and famous teachers, and is composed of vocational training, civil service examination, TOEFL IELTS, textual research grading and oral English.