JEE Main & Advanced Mathematics Inverse Trigonometric Functions Question Bank Critical Thinking

  • question_answer
    The equation \[2{{\cos }^{-1}}x+{{\sin }^{-1}}x=\frac{11\pi }{6}\]has [AMU 1999]

    A) No solution

    B) Only one solution

    C) Two solutions

    D) Three solutions

    Correct Answer: A

    Solution :

      Given equation is \[2{{\cos }^{-1}}x+{{\sin }^{-1}}x=\frac{11\pi }{6}\] Þ \[{{\cos }^{-1}}x+({{\cos }^{-1}}x+{{\sin }^{-1}}x)=\frac{11\pi }{6}\] Þ \[{{\cos }^{-1}}x+\frac{\pi }{2}=\frac{11\pi }{6}\] \[\Rightarrow {{\cos }^{-1}}x=4\pi /3\] which is not possible as \[{{\cos }^{-1}}x\in [0,\,\pi ]\].


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