It looks like you've uploaded an image with math problems written in Vietnamese. The problems refer to geometry and algebra.

The first problem (Bài 4) involves a right triangle with specific points and the goal is to prove several geometric identities and relations between them. The second problem (Bài 5) asks for a proof related to some algebraic expressions.

Would you like help solving these problems? If so, please specify which part you'd like to tackle first, or if you need a detailed breakdown of any part of the problem.