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Class 12 Continuity And Differentiability · Long Answer3 Marksbranch_sensitive_differentiation

Class 12 Maths · Continuity And Differentiability · Long Answer #82

For |x|>1, prove d(arcsec x)/dx=1/[|x|√(x²−1)].

✅ Step-by-Step Solution

Final Answer: 1/[|x|√(x²−1)]
  1. Let y=arcsec x on the principal range [0,π]∖{π/2}, so sec y=x.
  2. Differentiate: sec y tan y·y′=1. For x>1, both sec y,tan y are positive; for x<−1, both are negative.
  3. Thus sec y tan y=|sec y|·|tan y|=|x|√(x²−1), positive on both domain components.
  4. Therefore y′=1/[|x|√(x²−1)].

📋 CBSE Stepwise Marking Scheme

  • [0.5 marks] Let y=arcsec x on the principal range [0,π]∖{π/2}, so sec y=x.
  • [1 mark] Differentiate: sec y tan y·y′=1. For x>1, both sec y,tan y are positive; for x<−1, both are negative.
  • [1 mark] Thus sec y tan y=|sec y|·|tan y|=|x|√(x²−1), positive on both domain components.
  • [0.5 marks] Therefore y′=1/[|x|√(x²−1)].

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