This section deals with 2D shapes and angles related to them. It might be worth looking at the National 4 Angles section before continuing. For any triangle, the three angles add up to \(180^\circ\).

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 GOH = ...