JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Maxima and Minima

  • question_answer
    The sum of two numbers is fixed. Then its multiplication is maximum, when

    A)            Each number is half of the sum

    B)            Each number is \[\frac{1}{3}\]and  \[\frac{2}{3}\] respectively of the sum

    C)            Each number is \[\frac{1}{4}\] and \[\frac{3}{4}\] respectively of the sum

    D)            None of these

    Correct Answer: A

    Solution :

               Suppose that two numbers are \[x\]and \[y\].                    \[x+y=s\Rightarrow y=s-x\]                    Then \[f(x)=xy=x(s-x)=xs-{{x}^{2}}\]                    \[\therefore f'(x)=s-2x\]                    \[f'(x)=0\]for maximum value of \[f(x)\]                    \[\therefore x=\frac{s}{2}\] and \[y=\frac{s}{2}\]                    Thus each number is half of the sum.


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