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Class 12 Continuity And Differentiability · Short Answer2 Marksimplicit_differentiation

Class 12 Maths · Continuity And Differentiability · Short Answer #120

If sin²y+cos(xy)=K is constant, find dy/dx at x=1,y=π/4.

✅ Step-by-Step Solution

Final Answer: π/[4(√2−1)]
  1. Implicit differentiation gives 2sin y cos y·y′−sin(xy)(y+xy′)=0.
  2. At (1,π/4), this becomes y′−(√2/2)(π/4+y′)=0. Hence (1−√2/2)y′=π√2/8.
  3. Solving gives y′=π/[4(√2−1)].

📋 CBSE Stepwise Marking Scheme

  • [0.5 marks] Implicit differentiation gives 2sin y cos y·y′−sin(xy)(y+xy′)=0.
  • [1 mark] At (1,π/4), this becomes y′−(√2/2)(π/4+y′)=0. Hence (1−√2/2)y′=π√2/8.
  • [0.5 marks] Solving gives y′=π/[4(√2−1)].

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