IBDP Maths SL 3.4 The circle radian measure of angles AA HL Paper 2- Exam Style Questions- New Syllabus
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.
Find the area of the shaded region. [7]
▶️ Answer/Explanation
\(\alpha = 2\arcsin \left( {\frac{{4.5}}{7}} \right)\) (\( \Rightarrow \alpha = 1.396… = 80.010^\circ …\)) (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