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 = ...

Put more simply, angles in the same segment are equal. Let the obtuse angle MOQ = \(2x\). Using the circle theorem, the angle at the centre is twice the angle at the circumference. Angle MNQ = \(x\) ...