OR Let I_n = ∫(from 1 to √2) (x² - 1)ⁿ dx.
- (i)Show that, for n ≥ 1, (2n + 1)I_n = √2 – 2nI_n₋₁.[5]
- (ii)Using the substitution x = sec θ, show that I_n = ∫(from 0 to π/4) tan²ⁿ⁺¹ θ sec θ dθ.[4]
- (iii)Deduce the exact value of ∫(from 0 to π/4) sin⁷ θ / cos⁸ θ dθ.[5]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [M1A1] Integrates by parts.
- [M1] Uses x² = x² −1+1.
- [A1]
- [A1] AG.
- [M1A1] Differentiates secθ.
- [B1] Changes limits.
- [B1] Uses sec²θ−1 = tan² θ . (AG.)
- [B1] Deduces that integral is I₃.
- [B1] Calculates I₀ or I₁
- [M1A1] Uses reduction formula to find I₁ or I₂
- [A1] Finds I₂.
- [A1] Finds I₃.
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