Exam-Style Problem

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Nov 2013 p31 q6
1863

In the diagram, A is a point on the circumference of a circle with centre O and radius r. A circular arc with centre A meets the circumference at B and C. The angle OAB is θ radians. The shaded region is bounded by the circumference of the circle and the arc with centre A joining B and C. The area of the shaded region is equal to half the area of the circle.

(i) Show that \(\cos 2θ = \frac{2 \sin 2θ - π}{4θ}\).

(ii) Use the iterative formula \(θ_{n+1} = \frac{1}{2} \cos^{-1} \left( \frac{2 \sin 2θ_n - π}{4θ_n} \right)\), with initial value \(θ_1 = 1\), to determine \(θ\) correct to 2 decimal places, showing the result of each iteration to 4 decimal places.

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