If $f(2)=4$ and $f^{\prime}(2)=1$, then $$ \lim _{x \rightarrow 2} \frac{x f(2)-2 f(x)}{x-2} $$ is equal to

If $f(2)=4$ and $f^{\prime}(2)=1$, then $$ \lim _{x \rightarrow 2} \frac{x f(2)-2 f(x)}{x-2} $$ is equal to
  1. $-2$
  2. $1$
  3. $2$
  4. $3$

Solution

Given that, $f(2)=4$ and $f^{\prime}(2)=1$ $ \begin{aligned} \therefore \quad & \lim _{x \rightarrow 2} \frac{x f(2)-2 f(x)}{x-2} \\ & =\lim _{x \rightarrow 2} \frac{x f(2)-2 f(2)+2 f(2)-2 f(x)}{x-2} \\ = & \lim _{x \rightarrow 2} f(2)-2 \lim _{x \rightarrow 2} \frac{f(x)-f(2)}{x-2} \\ = & f(2)-2 f^{\prime}(2) \\ = & 4-2(1) \\ = & 2 \end{aligned} $

Asked in: AP EAMCET 2008

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