2025 NYJC Promo Q5

2025 NYJC Promo Q5

Junior College 1
8 marks
  1. Given that \(y=\cos^{-1}x\), show that \((1-x^2)\dfrac{d^2y}{dx^2}-x\dfrac{dy}{dx}=0\).[2]
  2. By differentiation of the result in part (a), find the first three non-zero terms of the Maclaurin expansion of \(\cos^{-1}x\). Give the coefficients in exact form.[3]
  3. Using your answer to part (b), find the series expansion of \(e^{\cos^{-1}x}\) up to and including the term in \(x^3\). Give the coefficients in terms of \(e\).[3]

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Answer:(b) \(\cos^{-1}x=\dfrac\pi2-x-\dfrac{x^3}{6}+\cdots\) (c) \(e^{\cos^{-1}x}=e^{\pi/2}(1-x+\dfrac{x^2}{2}-\dfrac{x^3}{3}+\cdots)\)

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