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Class 12 Continuity And Differentiability · Long Answer3 Marksimplicit_differentiation

Class 12 Maths · Continuity And Differentiability · Long Answer #80

If e^x+e^y=e^(x+y), prove y′+e^(y−x)=0.

✅ Step-by-Step Solution

Final Answer: y′=−e^(y−x)
  1. Differentiate implicitly: e^x+e^y y′=e^(x+y)(1+y′).
  2. Collect: [e^y−e^(x+y)]y′=e^(x+y)−e^x.
  3. Use e^(x+y)=e^x+e^y to replace the two sides by −e^x y′=e^y; since e^x>0, divide safely.
  4. Thus y′=−e^(y−x), proving the equation.

📋 CBSE Stepwise Marking Scheme

  • [0.5 marks] Differentiate implicitly: e^x+e^y y′=e^(x+y)(1+y′).
  • [1 mark] Collect: [e^y−e^(x+y)]y′=e^(x+y)−e^x.
  • [1 mark] Use e^(x+y)=e^x+e^y to replace the two sides by −e^x y′=e^y; since e^x>0, divide safely.
  • [0.5 marks] Thus y′=−e^(y−x), proving the equation.

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