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Class 12 Integrals · Long Answer3 Marksindefinite_integration

Class 12 Maths · Integrals · Long Answer #65

Evaluate \(\int \frac{1}{\sqrt{\sin^{3}{\left(x \right)} \cos{\left(a - x \right)}}}\,dx\). Work on real open intervals where sin³x cos(x−a)>0, assuming real a with cos a≠0.

✅ Step-by-Step Solution

Final Answer: \(- \frac{2 \sqrt{\sin{\left(a \right)} + \cos{\left(a \right)} \cot{\left(x \right)}}}{\cos{\left(a \right)}}\) + C
  1. Factor sin³x cos(x−a)=sin⁴x[sin a+cos a cot x]. For positive radicand, the integrand is csc²x/√(sin a+cos a cot x).
  2. Let u=√(sin a+cos a cot x). Then du=−cos a·csc²x dx/(2u).
  3. Thus the integral is −(2/cos a)∫du=−2u/cos a+C; substitute back.
  4. Therefore the required integral is \(- \frac{2 \sqrt{\sin{\left(a \right)} + \cos{\left(a \right)} \cot{\left(x \right)}}}{\cos{\left(a \right)}}\) + C.

📋 CBSE Stepwise Marking Scheme

  • [0.5 marks] Factor sin³x cos(x−a)=sin⁴x[sin a+cos a cot x]. For positive radicand, the integrand is csc²x/√(sin a+cos a cot x).
  • [1 mark] Let u=√(sin a+cos a cot x). Then du=−cos a·csc²x dx/(2u).
  • [1 mark] Thus the integral is −(2/cos a)∫du=−2u/cos a+C; substitute back.
  • [0.5 marks] Therefore the required integral is \(- \frac{2 \sqrt{\sin{\left(a \right)} + \cos{\left(a \right)} \cot{\left(x \right)}}}{\cos{\left(a \right)}}\) + C.

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