JEE Main & Advanced Mathematics Relations Question Bank Mock Test - Relations and Functions

  • question_answer
    Let \[f:\left[ -\frac{\pi }{3},\frac{2\pi }{3} \right]\to [0,4]\] be a function defined as \[f(x)=\sqrt{3}\sin x-\cos x+2\].Then \[{{f}^{-1}}(x)\]is given by

    A) \[{{\sin }^{-1}}\left( \frac{x-2}{2} \right)-\frac{\pi }{6}\]

    B) \[{{\sin }^{-1}}\left( \frac{x-2}{2} \right)+\frac{\pi }{6}\]

    C) \[\frac{2\pi }{3}+{{\cos }^{-1}}\left( \frac{x-2}{2} \right)\]

    D) none of these

    Correct Answer: B

    Solution :

    [b] \[y=f(x)=\sqrt{3}\sin x-\cos x+2\] \[=2\sin \left( x-\frac{\pi }{6} \right)+2\]                     ...(1) Since \[f(x)\]is one-one and onto, f is invertible. From (1), \[\sin \left( x-\frac{\pi }{6} \right)=\frac{y-2}{2}\] Or  \[x={{\sin }^{-1}}\frac{y-2}{2}+\frac{\pi }{6}\] Or  \[{{f}^{-1}}(x)=si{{n}^{-1}}\left( \frac{x-2}{2} \right)+\frac{\pi }{6}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner