J & K CET Engineering J and K - CET Engineering Solved Paper-2004

  • question_answer
    If \[f(x)\] is a differentiable function, then \[\underset{x\to a}{\mathop{\lim }}\,\frac{af\,(x)-x\,f(a)}{x-a}\] is equal to

    A)  \[af'\,(a)-f(a)\]

    B)  \[af\,\,(a)+f'(a)\]  

    C)  \[af'\,(a)+f(a)\]

    D)  \[af\,(a)-f'(a)\]

    Correct Answer: A

    Solution :

    \[\underset{x\to a}{\mathop{\lim }}\,\frac{af\,(x)-xf(a)}{x-a}\] \[=\underset{x\to a}{\mathop{\lim }}\,\frac{af\,(x)-af(a)+af(a)-xf(a)}{x-a}\] \[\underset{x\to a}{\mathop{\lim }}\,\frac{a[f\,(x)-f(a)]}{x-a}-\underset{x\to a}{\mathop{\lim }}\,\,f(x)\] \[af'\,(a)-f(a)\]


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