Geometry · Tangent circles · Angle in a semicircle · Isosceles triangle · Angle bisector

Problem 2, 2007

← Prev · 324 / 651 · Next →

RegionalProof

Two circles touch each other internally at a point \(A\). Let \(AB\) be a diameter of the larger circle. Through the other endpoint \(B\) of this diameter a line is drawn which touches the smaller circle at a point \(C\) and meets the larger circle again at a point \(D\).

Prove that the line \(AC\) bisects the angle \(BAD\).

A B C D
The two circles touch internally at \(A\), the segment \(AB\) is a diameter of the larger one, the line through \(B\) touches the smaller circle at \(C\), and \(D\) is where it meets the larger circle a second time.

Sign in to check answers, open hints, read the full solution, and track your progress. Statements are always free.

Serbian Regional Competition 2007, high school grade I, category A, problem 2. Organized by the Mathematical Society of Serbia (DMS). Source