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NCERT Class 12 · Ch 5 Exercise 5.7 · Q6

NCERT Class 12 Maths · Chapter 5 Continuity And Differentiability · Exercise 5.7 Question 6

Find the second derivative of \(e^{x} \sin{\left(5 x \right)}\) with respect to x; on R.

💡 Concept Hints

  1. Identify the domain and the inner and outer functions, or the relevant one-sided limits.
  2. Apply the appropriate differentiation or limit rule, keep all chain factors, and check exceptional points.

✅ Step-by-Step Solution

Final Answer: \(2 \left(- 12 \sin{\left(5 x \right)} + 5 \cos{\left(5 x \right)}\right) e^{x}\)
  1. Work on R.
  2. Product rule: differentiate each variable factor once, keeping the other factors unchanged. Here \(\frac{d}{d x} e^{x} \sin{\left(5 x \right)}\) = \(e^{x} \sin{\left(5 x \right)} + 5 e^{x} \cos{\left(5 x \right)}\).
  3. Differentiate the first derivative \(e^{x} \sin{\left(5 x \right)} + 5 e^{x} \cos{\left(5 x \right)}\) again.
  4. Product rule: differentiate each variable factor once, keeping the other factors unchanged. Here \(\frac{d}{d x} e^{x} \sin{\left(5 x \right)}\) = \(e^{x} \sin{\left(5 x \right)} + 5 e^{x} \cos{\left(5 x \right)}\).
  5. Product rule: differentiate each variable factor once, keeping the other factors unchanged. Here \(\frac{d}{d x} 5 e^{x} \cos{\left(5 x \right)}\) = \(- 25 e^{x} \sin{\left(5 x \right)} + 5 e^{x} \cos{\left(5 x \right)}\).
  6. Sum rule: \(\frac{d}{d x} \left(e^{x} \sin{\left(5 x \right)} + 5 e^{x} \cos{\left(5 x \right)}\right)\) = \(- 24 e^{x} \sin{\left(5 x \right)} + 10 e^{x} \cos{\left(5 x \right)}\).
  7. Combining the terms gives y″ = \(2 \left(- 12 \sin{\left(5 x \right)} + 5 \cos{\left(5 x \right)}\right) e^{x}\).

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