Circle

Step 1: Understanding the Geometry
Let the radius of the circle be , and let the length of the chord be as well.
The central angle subtended by the chord can be determined using the cosine rule in the triangle formed by the radius lines and the chord.
Step 2: Apply the Cosine Rule
In the isosceles triangle formed by the two radii and the chord, the angle at the center satisfies: Thus, , and hence .
Step 3: Conclusion
Thus, the angle subtended at the center of the circle by the chord is .