JEE Main & Advanced Mathematics Limits, Continuity and Differentiability Question Bank Self Evaluation Test - Continuity and Differentiability

  • question_answer
    The number of points in (1, 3), where \[f(x)={{a}^{[{{x}^{2}}]}},a>1\], is not differentiable, where [x] denotes the integral part of x.

    A) 5

    B) 7

    C) 9

    D) 11

    Correct Answer: B

    Solution :

    [b] Here \[1<x<3\] and in this interval \[{{x}^{2}}\] is an increasing functions, thus, \[1<{{x}^{2}}<9\] \[[{{x}^{2}}]=1,1\le x<\sqrt{2}=2,\sqrt{2}\le x<\sqrt{3}\] \[=3,\sqrt{3}\le x<2=4,2\le x<\sqrt{5}\] \[=5,\sqrt{5}\le x<\sqrt{6}=6,\sqrt{6}\le x<\sqrt{7}\] \[=7\sqrt{7}\le x<\sqrt{8}=8,\sqrt{8}\le x<3\] Clearly, \[[{{x}^{2}}]\] and also \[{{a}^{[{{x}^{2}}]}}\] is discontinuous and not differentiable at only 7 points, \[x=\sqrt{2},\sqrt{3},2,\sqrt{5},\sqrt{6}\sqrt{7},\sqrt{8}\]


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