The angle subtended close subtendAn angle created by an object at a given point. by an arc close arcThe curve between two points on the circumference of a circle. at the centre is twice the angle ...

More simply, the angle at the centre is double the angle at the circumference. Angle OGH (\(y\)) = angle OHG because triangle GOH is also isosceles. Lengths OH and OG are also both radii. Angle ...