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

  • question_answer
    If from a wire of length 36 metre a rectangle of greatest area is made, then its two adjacent sides in metre are                                                                                            [MP PET 1998]

    A)            6, 12

    B)            9, 9

    C)            10, 8

    D)            13, 5

    Correct Answer: B

    Solution :

               Given         \[2(a+b)=36\],  \[a+b=18\]                    Area of rectangle \[=ab=a(18-a)\]                    \[A=18a-{{a}^{2}}\,,\,\,\therefore \frac{dA}{da}=18-2a\]                    Put \[\frac{dA}{da}=0\]  i.e., \[18-2a=0\ \ \Rightarrow \,a=9;\,\ b=9\].


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