JEE Main & Advanced Mathematics Functions Question Bank Self Evaluation Test - Relation and Functions-II

  • question_answer
    The domain of the function\[f(x){{=}^{24-x}}{{C}_{3x-1}}{{+}^{40-6x}}{{C}_{8x-10}}\] is,

    A) \[\{2,3\}\]

    B) \[\{1,2,3\}\]

    C) \[\{1,2,3,4\}\]

    D) None of these

    Correct Answer: A

    Solution :

    [a] \[^{24-x}{{C}_{3x-1}}\] is defined if,
    \[24-x>0,3x-1\ge 0\] And \[24-x\ge 3x-1\]
    \[\Rightarrow x<24,x\ge \frac{1}{3}\] And \[x\le \frac{25}{4}\Rightarrow \frac{1}{3}\le x\le \frac{25}{4}\]
    \[^{40-6x}{{C}_{8x-10}}\] is defined if
    \[40-6x>0,8x-10\ge 0\] And \[40-6x\ge 8x-10\]
    \[\Rightarrow x<\frac{20}{3},x\ge \frac{5}{4}andx\le \frac{25}{7}\]
    \[\Rightarrow \frac{5}{4}\le x\le \frac{25}{7}\]
    From (1) and (2), we get \[\frac{5}{4}\le x\le \frac{25}{7}\]
    But \[24-x\in N,\therefore x\]must be an integer, \[x=2,3.\]
    Hence domain \[(f)=\{2,\,\,3\}.\]


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