I see you've uploaded an image with a geometry problem in Vietnamese. Let me break it down and provide a translation of the problem first:

Problem:

Given a circle $(O; R)$ and a point $A$ outside the circle $(O)$. From point $A$, two tangents $AB$ and $AC$ are drawn to the circle, where points $B$ and $C$ are the tangent points. Let $H$ be the intersection of the lines $OA$ and $BC$, and the extension of the line $AD$ intersects the circle again at point $E$ (different from $D$).

Tasks: a) Prove that the points $A, B, C, O$ lie on the same circle. Determine the center and the radius of that circle.

b) Prove that the line $OA$ is perpendicular to the line $BC$ at $H$.

c) Prove that the line $OA$ is equal to $1/CD$.

d) When $OA = BD$, calculate the radius of the circle $R$ using the information given and the intersection of the lines $OC$, $OD$, and the arc of $CD$.

Do you want me to walk through the solution step by step or explain any part in more detail? Let me know if you'd like me to continue!