Let $f:(-\infty, \infty)-\{0\} \rightarrow \mathbb{R}$ be a differentiable function such that $f^{\prime}(1)=\lim _\limits{a \rightarrow \infty} a^2 f\left(\frac{1}{a}\right)$. Then $$\lim _\limits{a \rightarrow \infty} \frac{a(a+1)}{2} \tan ^{-1}\left(\frac{1}{a}\right)+a^2-2 \log _e a$$ is equal to
Solution
<p>Let $f^{\prime}(1)=k$</p>
<p>$$\Rightarrow \quad \lim _\limits{x \rightarrow 0} \frac{f(x)}{x^2}=k \quad\left(\frac{0}{0}\right)$$</p>
<p>$$\begin{aligned}
& \lim _\limits{x \rightarrow 0} \frac{f^{\prime}(x)}{2 x}=\lim _{x \rightarrow 0} \frac{f^{\prime \prime}(x)}{2}=k \\
\Rightarrow & f^{\prime \prime}(0)=2 k
\end{aligned}$$</p>
<p>Given information is not complete.</p>
About this question
Subject: Mathematics · Chapter: Differentiation · Topic: Derivatives of Standard Functions
This question is part of PrepWiser's free JEE Main question bank. 55 more solved questions on Differentiation are available — start with the harder ones if your accuracy is >70%.