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NCERT Class 12 · Ch 9 Exercise 9.4 · Q13

NCERT Class 12 Maths · Chapter 9 Differential Equations · Exercise 9.4 Question 13

Show the equation y′=\(- \sin^{2}{\left(\frac{y}{x} \right)} + \frac{y}{x}\) is homogeneous and solve it. Initial condition: y(1)=π/4.

💡 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: cot(y/x)=log x+1 on the initial branch.
  1. After division the slope depends only on y/x (on a fixed sign component when radicals occur). Put y=vx, so y′=v+xv′.
  2. The reduced equation is x dv/dx=\(- \sin^{2}{\left(v \right)}\). Separate dv/(\(- \sin^{2}{\left(v \right)}\))=dx/x on branches where division is valid.
  3. Integration and back-substitution give \(- \log{\left(\left|{x}\right| \right)} + \cot{\left(\frac{y}{x} \right)}\) = C.
  4. Separate −cosec²v dv=dx/x. At x=1,y=π/4 the constant is 1.
  5. Differentiate the resulting relation to recover the equation on intervals where the original expressions and the required slope are defined.

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