Question

How do you find the first and second derivative of $y=2\ln \left( x \right)$?

Answer 1

Hint: The differentiation of the given function $y=2\ln \left( x \right)$ will be defined as ${{f}^{'}}\left( x \right)$ and ${{f}^{''}}\left( x \right)$ respectively where $y=f\left( x \right)=2\ln \left( x \right)$. We differentiate the given function $y=2\ln \left( x \right)$ with $x$. The differentiated forms are $\dfrac{d}{dx}\left[ \ln \left( x \right) \right]=\dfrac{1}{x}$ and $\dfrac{d}{dx}\left[ \dfrac{1}{x} \right]=\dfrac{-1}{{{x}^{2}}}$. We use those forms and keep the constants as it is.

Complete step by step answer:
In case of finding any derivative, we have to differentiate the given function $y=2\ln \left( x \right)$ with $x$. Let’s assume that $y=f\left( x \right)=2\ln \left( x \right)$. The given function is a function of $x$.
The first derivative is $\dfrac{dy}{dx}=\dfrac{d}{dx}\left[ f\left( x \right) \right]$. It’s also defined as ${{f}^{'}}\left( x \right)$.
The differentiated form of $\ln \left( x \right)$ is $\dfrac{d}{dx}\left[ \ln \left( x \right) \right]=\dfrac{1}{x}$. The constant remains as it is.
There is a function $af\left( x \right)$ where $a$ is a constant. If we are going to differentiate the function the formula remains as $\dfrac{d}{dx}\left[ af\left( x \right) \right]=a\dfrac{d}{dx}\left[ f\left( x \right) \right]$.
Therefore, the first derivative of $y=2\ln \left( x \right)$ is ${{f}^{'}}\left( x \right)=\dfrac{d}{dx}\left[ 2\ln \left( x \right) \right]=\dfrac{2}{x}$.
Now we need to find the second derivative.
The second derivative is $\dfrac{d}{dx}\left[ {{f}^{'}}\left( x \right) \right]$. It’s also defined as ${{f}^{''}}\left( x \right)$.
The differentiation of constants has been discussed before.
The differentiated form of \[\dfrac{1}{x}\] is $\dfrac{d}{dx}\left[ \dfrac{1}{x} \right]=\dfrac{-1}{{{x}^{2}}}$. The constant remains as it is.
Therefore, the second derivative of ${{f}^{'}}\left( x \right)=\dfrac{2}{x}$ is \[{{f}^{''}}\left( x \right)=\dfrac{d}{dx}\left[ \dfrac{2}{x} \right]=\dfrac{-2}{{{x}^{2}}}\].
The first and second derivative of the given function $y=2\ln \left( x \right)$ is $\dfrac{2}{x}$ and \[\dfrac{-2}{{{x}^{2}}}\] respectively.

Note: The second derivative can also be expressed as $\dfrac{{{d}^{2}}y}{d{{x}^{2}}}=\dfrac{d}{dx}\left( \dfrac{dy}{dx} \right)$. The differentiation $\dfrac{d}{dx}\left[ \dfrac{1}{x} \right]=\dfrac{-1}{{{x}^{2}}}$ has been done following the rule of exponent where $\dfrac{d}{dx}\left[ {{x}^{n}} \right]=n{{x}^{n-1}}$. Here the value of n was -1 as ${{x}^{-1}}=\dfrac{1}{x}$.