Skip to content / Đến nội dung
ThichHocToan.com

MathNet 2023-part-06 — 191 problems (EN–VI) Question 1

Math Olympiad Vault · MathNet 2023-part-06 — 191 problems (EN–VI)

Question 1

Given two circles $(O_1), (O_2)$ with different radii and intersecting at two points $A, B$. The tangent $CD$ of the two circles (closer to point $B$) with $C \in (O_1)$ and $D \in (O_2)$. Draw diameters $BP, BQ$ of $(O_1), (O_2)$. The line through $B$, and perpendicular to $CD$ cuts $PQ$ at $K$.

a) Prove that $B$ is the orthocenter of triangle $KCD$.

b) Draw the angle bisectors $BX, BY$ of the triangles $KBP, KBQ$ respectively with $X, Y \in PQ$. Prove that $KX = KY$.