is a point on the diagonal of the square . Show that the points and the circumcenters of and form a square.
Solution
1. Define the points and circumcenters:
Let and be the circumcenters of the triangles and , respectively. We need to show that the points and form a square.
2. Circumradius equality:
Let and be the lengths of the circumradii of the triangles and , respectively. Using the Law of Sines in triangles and , we have:
Since (both are sides of the square ) and (as lies on the diagonal ), it follows that:
Therefore, the circumradii are equal, and we have:
3. Angle calculation:
Next, we need to show that . The angle subtended by the arc in the circumcircle of is twice the angle at :
Since (as is a right triangle with being half of ), we have:
4. Conclusion:
From the equal circumradii and the right angle, we conclude that is a square. The sides are equal, and the angles are right angles.