The curve C has parametric equations x = 4t + 2t³, y = 4t - 2t², for 0 ≤ t ≤ 4. Find the arc length of C, giving your answer correct to 3 significant figures. Find the mean value of y with respect to x over the interval 0 ≤ x ≤ 32.
Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- [B1] ẋ = 4 + 3t², ẏ = 4 - 3t²
- [B1] ẋ² + ẏ² = 32 + 18t
- [M1A1] s = ∫₀⁴ (32+18t)¹/² dt = 1/27 (32+18t)³/² |₀⁴
- [M1A1] = 1/27 (104³/² - 32³/²) = 32.6 (CAO)
- [M1] ∫ y dx = ∫₀⁴ y (dx/dt) dt = ∫₀⁴ (4t-2t²)(4+3t²) dt = ∫₀⁴ (16t+4t²-6t³) dt
- [M1A1] = [8t²+4/3 t³ - 3/2 t⁴] |₀⁴ = 51.2
- [M1A1] MV = ∫ y dx / (b-a) = 51.2 / 32 = 1.6 (CAO)
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