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NCERT Class 12 · Ch 5 Exercise 5.6 · Q7

NCERT Class 12 Maths · Chapter 5 Continuity And Differentiability · Exercise 5.6 Question 7

Without eliminating parameter t (θ in the trigonometric source forms), find dy/dx for x=\(\frac{\sin^{3}{\left(t \right)}}{\sqrt{\cos{\left(2 t \right)}}}\), y=\(\frac{\cos^{3}{\left(t \right)}}{\sqrt{\cos{\left(2 t \right)}}}\).

💡 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: \(- \frac{2 \cos{\left(2 t \right)} - 1}{\left(2 \cos{\left(2 t \right)} + 1\right) \tan{\left(t \right)}}\) where the real parametrisation is defined and dx/dt≠0.
  1. Differentiate both coordinates: dx/dt=\(\frac{\sin^{3}{\left(t \right)} \sin{\left(2 t \right)}}{\cos^{\frac{3}{2}}{\left(2 t \right)}} + \frac{3 \sin^{2}{\left(t \right)} \cos{\left(t \right)}}{\sqrt{\cos{\left(2 t \right)}}}\), dy/dt=\(- \frac{3 \sin{\left(t \right)} \cos^{2}{\left(t \right)}}{\sqrt{\cos{\left(2 t \right)}}} + \frac{\sin{\left(2 t \right)} \cos^{3}{\left(t \right)}}{\cos^{\frac{3}{2}}{\left(2 t \right)}}\).
  2. Divide the two rates: dy/dx=(dy/dt)/(dx/dt)=\(\frac{- \frac{3 \sin{\left(t \right)} \cos^{2}{\left(t \right)}}{\sqrt{\cos{\left(2 t \right)}}} + \frac{\sin{\left(2 t \right)} \cos^{3}{\left(t \right)}}{\cos^{\frac{3}{2}}{\left(2 t \right)}}}{\frac{\sin^{3}{\left(t \right)} \sin{\left(2 t \right)}}{\cos^{\frac{3}{2}}{\left(2 t \right)}} + \frac{3 \sin^{2}{\left(t \right)} \cos{\left(t \right)}}{\sqrt{\cos{\left(2 t \right)}}}}\).
  3. Simplify to \(- \frac{2 \cos{\left(2 t \right)} - 1}{\left(2 \cos{\left(2 t \right)} + 1\right) \tan{\left(t \right)}}\). This quotient requires dx/dt≠0; any cancelled zero requires a separate limiting or curve check.

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