Let Iⁿ = ∫(from 0 to π/4) secⁿx dx for n > 0.
- (i)Find the value of I₂.[2]
- (ii)Show that, for n > 2, (n - 1)Iⁿ = 2ⁿ⁻¹ + (n - 2)Iⁿ⁻².[5]
- (iii)The curve C has equation y = sec³x for 0 ≤ x ≤ π/4. The region R is bounded by C, the x-axis, the y-axis and the line x = π/4. Find the volume of revolution generated when R is rotated through 2π radians about the x-axis.[4]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- [2] M1A1
- [1] M1 For setting up integration by parts (u = secⁿ⁻²x, dv/dx = sec²x)
- [2] M1A1 For applying integration by parts: [secⁿ⁻²x tanx] - ∫ (n-2)secⁿ⁻²x tan²x dx
- [1] M1 For using tan²x = sec²x - 1 and splitting the integral
- [1] A1 AG For rearranging and showing (n - 1)Iⁿ = 2ⁿ⁻¹ + (n - 2)Iⁿ⁻²
- [1] M1
- [1] M1
- [1] M1
- [1] A1
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