Home / IBDP Maths SL 3.4 The circle radian measure of angles AA HL Paper 2- Exam Style Questions

IBDP Maths SL 3.4 The circle radian measure of angles AA HL Paper 2- Exam Style Questions

IBDP Maths SL 3.4 The circle radian measure of angles AA HL Paper 2- Exam Style Questions- New Syllabus

Question

The radius of the circle with centre C is 7 cm and the radius of the circle with centre D is 5 cm. If the length of the chord [AB] is 9 cm, find the area of the shaded region enclosed by the two arcs AB.

Circle diagram

Find the area of the shaded region. [7]

▶️ Answer/Explanation
Markscheme

Solution diagram

\(\alpha = 2\arcsin \left( {\frac{{4.5}}{7}} \right)\) (\( \Rightarrow \alpha = 1.396… = 80.010^\circ …\)) (M1)(A1)

\(\beta = 2\arcsin \left( {\frac{{4.5}}{5}} \right)\) (\( \Rightarrow \beta = 2.239… = 128.31^\circ …\)) (A1)

Note: Allow use of cosine rule.

Area \(P = \frac{1}{2} \times {7^2} \times \left( {\alpha – \sin \alpha } \right) = 10.08…\) (M1)(A1)

Area \(Q = \frac{1}{2} \times {5^2} \times \left( {\beta – \sin \beta } \right) = 18.18…\) (A1)

Note: The M1 is for an attempt at area of sector minus area of triangle.

Note: The use of degrees correctly converted is acceptable.

Total area = 28.3 (cm²) (A1)

[7 marks]

Key Concepts

\(\text{Segment area} = \frac{1}{2}r^2(\theta – \sin\theta)\)

\(\theta = 2\arcsin\left(\frac{\text{half chord}}{r}\right)\)

Consistent units (radians/degrees) must be maintained

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