Teacher Zhang Xu's class in Taiwan Province Province is on Mile Mile, YouTube and Facebook. Zhang Xu's job is to be a teacher in the extra-curricular class of advanced mathematics in Taiwan Province Province. Because she posted her teaching video to Pornhub, the world's largest pornographic website, she unexpectedly gained the attention of many advanced mathematics learners at home and abroad. The seemingly ridiculous thing hides the powerful logical thinking of the math teacher. At first, he recorded online videos to recruit students, but the videos he posted on YouTube and Facebook didn't bring much hits, because the volume of the teaching and training circle was too serious, and there were too many teaching videos about advanced mathematics on such websites.