The curve C has polar equation r = a(1 + sin θ), where a is a positive constant and 0 ≤ θ < 2π. Draw a sketch of C. Find the exact value of the area of the region enclosed by C and the half-lines θ = π/4 and θ = π.
- The curve C has polar equation r = a(1 + sin θ), where a is a positive constant and 0 ≤ θ < 2π. Draw a sketch of C.[2]
- Find the exact value of the area of the region enclosed by C and the half-lines θ = π/4 and θ = π.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.
- [B1] Closed curve through (a, 0), (2a, π/2), (a, π), (0, 3π/2).
- [B1] Completely correct shape for cardioid.
- [M1] Area = ½ ∫(π, π/4) r² dθ = ½ ∫(π, π/4) a²(1 + sin θ)² dθ (LNR)
- [M1] = ½ a² ∫(π, π/4) (1 + 2 sin θ + sin² θ) dθ
- [M1] = ½ a² ∫(π, π/4) (3/2 + 2 sin θ – ½ cos 2θ) dθ (LR)
- [A1] = a²/2 [ (3/2)θ – 2 cos θ – (1/4) sin 2θ ] (π, π/4)
- [A1] = a² (9π/16 + 9/8 + √2/2) (CAO)
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