Mr. Li Yongle helps you to learn the Circle's Area Formula & principles of calculus in 4 mins!

Hot video recommendation: Why is Gleevec in "Dying to Survive" so expensive? Is generic medicine a fake?
Video link: • 《我不是药神》里的格列卫凭什么这么贵？仿制药...
This is a new cut of an old one.