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BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    If the rate of change of area of a square plate is 13 equal to that of the rate of change of its perimeter, then length of the side is

    A) 1 unit                    

    B) 2 units

    C) 3 units                  

    D) 4 units

    Correct Answer: B

    Solution :

    Let at any time t, the length of a side of the square be \[x\]. Then, \[A=Area={{x}^{2}}\] and        \[\text{P = Perimeter = }4x\] \[\Rightarrow \]               \[\frac{dA}{dt}=2x\frac{dx}{dt}\]and \[\frac{dP}{dt}=4\frac{dx}{dt}\] It is given that                                 \[\frac{dA}{dt}=\frac{dP}{dt}\] \[\Rightarrow \]               \[2x\frac{dx}{dt}=4\frac{dx}{dt}\Rightarrow x=2\]


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