JEE Main & Advanced Mathematics Differentiation Question Bank Derivative at a point Standard Differentiation

  • question_answer
    The derivative of \[y=(1-x)\,(2-x)....(n-x)\] at \[x=1\] is equal to                                     [Kerala (Engg.) 2005]

    A)            0

    B)            \[(-1)\,(n-1)\,!\]

    C)            \[n!\,-\,1\]

    D)            \[{{(-1)}^{n-1}}(n-1)\,!\]

    E)            \[{{(-1)}^{n}}\,(n-1)\,!\]

    Correct Answer: B

    Solution :

               \[\frac{dy}{dx}=-[(2-x)(3-x).....(n-x)+(1-x)(3-x)....(n-x)\]                                \[+.....(1-x)(2-x).....(n-1-x)]\]at \[x=1\]                    \[\frac{dy}{dx}=-[(n-1)!+0+.......+0]\]\[=(-1)n-1\ !\]


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