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

  • question_answer
    Let\[f :X\to y\,f(x)=sinx+cosx+2\sqrt{2}\]be invertible. Then which \[X\to Y\]is not possible?

    A) \[\left[ \frac{\pi }{4},\frac{5\pi }{4} \right]\to [\sqrt{2},3\sqrt{2}]\]

    B) \[\left[ -\frac{3\pi }{4},\frac{\pi }{4} \right]\to [\sqrt{2},3\sqrt{2}]\]

    C) \[\left[ -\frac{3\pi }{4},\frac{3\pi }{4} \right]\to [\sqrt{2},3\sqrt{2}]\]

    D) none of these

    Correct Answer: C

    Solution :

    [c] \[f(x)=\sqrt{2}\sin \left( x+\frac{\pi }{4} \right)+2\sqrt{2}\] Or \[f(x)=\sqrt{2}\cos \left( x-\frac{\pi }{4} \right)+2\sqrt{2}\] i.e., \[Y=[\sqrt{2},3\sqrt{2}]\] and \[X=\left[ -\frac{3\pi }{4},\frac{\pi }{4} \right]\] or \[\left[ \frac{\pi }{4},\frac{5\pi }{4} \right]\]


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