It is given that y = eˣu, where u is a function of x. The rth derivatives dʳy/dxʳ and dʳu/dxʳ are denoted by y⁽ʳ⁾ and u⁽ʳ⁾ respectively. Prove by mathematical induction that, for all positive integers n, y⁽ⁿ⁾ = eˣ ((ⁿ₀) u + (ⁿ₁) u⁽¹⁾ + (ⁿ₂) u⁽²⁾ + ... + (ⁿᵣ) u⁽ʳ⁾ + ... + (ⁿₙ) u⁽ⁿ⁾). [You may use without proof the result (ᵏᵣ) + (ᵏᵣ₋₁) = (ᵏ⁺¹ᵣ)].
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [M1A1] Shows base case using product rule
- [B1] States inductive hypothesis.
- [M1] Differentiates using product rule
- [M1A1] Shows application of (k r) + (k r-1) = (k+1 r).
- [B1] Shows reasoning for first and last term correctly
- [A1] States conclusion.
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