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Class 12 Inverse Trigonometric Functions · Long Answer3 Marksprincipal_values

Class 12 Maths · Inverse Trigonometric Functions · Long Answer #100

Evaluate \(2\cos^{-1}(1/2)+2\sin^{-1}(-1/2)-\cos^{-1}(-1)\).

✅ Step-by-Step Solution

Final Answer: −2π/3
  1. The principal values are arccos(1/2)=π/3, arcsin(−1/2)=−π/6 and arccos(−1)=π.
  2. Substitute to obtain 2π/3+2(−π/6)−π.
  3. This simplifies to 2π/3−π/3−π=π/3−π.
  4. The correct value is −2π/3.

📋 CBSE Stepwise Marking Scheme

  • [0.5 marks] The principal values are arccos(1/2)=π/3, arcsin(−1/2)=−π/6 and arccos(−1)=π.
  • [1 mark] Substitute to obtain 2π/3+2(−π/6)−π.
  • [1 mark] This simplifies to 2π/3−π/3−π=π/3−π.
  • [0.5 marks] The correct value is −2π/3.

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