JEE Main & Advanced Mathematics Inverse Trigonometric Functions Question Bank Self Evaluation Test - Inverse Trigonometric Functions

  • question_answer
    If \[{{\sin }^{-1}}a+{{\sin }^{-1}}b+{{\sin }^{-1}}c=\pi ,\] then find the value of\[a\sqrt{1-{{a}^{2}}}+b\sqrt{1-{{b}^{2}}}+c\sqrt{1-{{c}^{2}}}.\]

    A) \[abc\]

    B) \[a+b+c\]

    C) \[\frac{1}{a}\times \frac{1}{b}\times \frac{1}{c}\]

    D) \[2abc\]

    Correct Answer: D

    Solution :

    [d] Let \[{{\sin }^{-1}}a=x\]     \[\therefore a=\sin x\] \[{{\sin }^{-1}}b=y\]    \[\therefore b=\sin y;{{\sin }^{-1}}c=z\] \[\therefore c=\sin z\] \[\therefore a\sqrt{1-{{a}^{2}}}+b\sqrt{1-{{b}^{2}}}+c\sqrt{1-{{c}^{2}}}\] \[=\sin x\cos x+\sin y\cos y+\operatorname{sinzcosz}\] \[=(1/2)(sin2x+sin2y+sin2z)=(1/2)(4sinxsinysinz)\]\[=2\sin x\sin y\sin z=2abc\]


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