Solved Examples on Logarithmic Differentiation
Example 1: Find the derivative of xx.
Solution:
Let y = xx
Step 1: Taking log on both sides
log(y) = log(xx)
Step 2: Use logarithmic property to simplify the equation
log(y) = x ⋅ log(x) [Using property log(ab) = b⋅ log(a)]
Step 3: Now differentiate the equation with respect to x,
[Tex]\frac{d}{d x} \log (y)=\frac{d}{d x}(x \cdot \log (x)) \\ \frac{d}{d x} \log (y)=x \cdot \frac{d}{d x} \log (x)+\log (x) \cdot \frac{d x}{d x} \\ \frac{1}{y} \frac{d y}{d x}=x \cdot \frac{1}{x}+\log (x) [/Tex]
Step 4: Simplify the obtained equation
[Tex]\frac{d y}{d x}=y(1+\log (x)) [/Tex]
Step 5: Substitute back the value of y
[Tex]\frac{d y}{d x}=x^{x}(1+\log (x)) [/Tex]
Example 2: Find the derivative of [Tex]x^{\left(x^{x}\right)} [/Tex]?
Solution:
Given,
y = [Tex]x^{\left(x^{x}\right)} [/Tex]
Step 1: Taking log on both sides,
log(y) = log([Tex]x^{\left(x^{x}\right)} [/Tex])
Step 2: Use logarithmic property to simplify the equation
log(y) = xx⋅ log(x) [Using property log(ab) = b⋅ log(a)]
Step 3: Differentiating both sides with respect to x,
[Tex]\frac{d}{d x} \log (y)=\frac{d}{d x}\left(x^{x} \cdot \log (x)\right) \\ \frac{d}{d x} \log (y)=x^{x} \cdot \frac{d}{d x} \log (x)+\log (x) \cdot \frac{d}{d x} x^{x}\left\{f^{\prime}(u . v)=u . f^{\prime}(v)+v \cdot f^{\prime}(u)\right\} \\ \frac{1}{y} \frac{d y}{d x}=x^{x} \cdot \frac{1}{x}+\log (x) \frac{d}{d x} x^{x} \left\{f^{\prime}(\log x)=\frac{1}{x}\right\}\\ \frac{1}{y} \frac{d y}{d x}=x^{x-1}+\log (x) \frac{d}{d x} x^{x} [/Tex]
Step 4: Simplify the obtained equation,
Since now we know the derivative of xx, We will substitute here directly.
[Tex] \frac{1}{y} \frac{d y}{d x}=x^{x-1}+\log x \cdot x^{x}(1+\log x) \\ \frac{d y}{d x}=y\left(x^{x-1}+\log x \cdot x^{x}(1+\log x)\right) [/Tex]
Step 5: Substitute back the value of y
[Tex] \frac{d y}{d x}=x^{\left(x^{x}\right)}\left(x^{x-1}+\log x \cdot x^{x}(1+\log x)\right) [/Tex]
Example 3: Find the derivative of y = (log x)x.
Solution:
Given,
y = (logx)x
Step 1: Taking log on both sides,
log(y) = log((logx)x)
Step 2: Use logarithmic property to simplify the equation
log(y) = x ⋅ log(logx) [using property log(ab) = b⋅ log(a)]
Step 3: Differentiating both sides with respect to x,
[Tex]\frac{d}{d x} \log (y)=\frac{d}{d x}(x \cdot \log (\log x)) \\ \frac{d}{d x} \log (\mathrm{y})=x \cdot \frac{d}{d x} \log (\log x)+\log (\log x) \cdot \frac{d x}{d x} \\ \frac{1}{y} \frac{d y}{d x}=x \cdot \frac{1}{\log x} \cdot \frac{1}{x}+\log (\log x) [/Tex]
Step 4: Simplify the obtained equation,
[Tex] \frac{1}{y} \frac{d y}{d x}=\frac{1}{\log x}+\log (\log x) \{ using~chain~rule \} \\ \frac{d y}{d x}=y \cdot\left(\frac{1}{\log x}+\log (\log x)\right) \\ [/Tex]
Step 5: Substitute back the value of y
[Tex]\frac{d y}{d x}=(\log x)^{x} \cdot\left(\frac{1}{\log x}+\log (\log x)\right) [/Tex]
Example 4: Find the derivative of y = x√x.
Solution:
Given,
y = x√x
Step 1: Taking log on both sides,
log(y) = log(x√x)
Step 2: Use logarithmic property to simplify the equation
log(y) = √x⋅ log(x) [using property log(ab) = b⋅ log(a)]
Step 3: Differentiating both sides with respect to x,
[Tex]\frac{d}{d x} \log (y)=\frac{d}{d x}(\sqrt{x} \cdot \log (x))\\ \frac{d}{d x} \log (\mathrm{y})=\sqrt{x} \cdot \frac{d}{d x} \log (\mathrm{x})+\log (x) \cdot \frac{d \sqrt{x}}{d x} [/Tex]
Step 4: Simplify the obtained equation,
[Tex] \frac{1}{y} \frac{d y}{d x}=\sqrt{x} \cdot \frac{1}{x}+\log (x) \cdot \frac{1}{2 \sqrt{x}} \\ \frac{1}{y} \frac{d y}{d x}=\frac{1}{\sqrt{x}}+\log (x) \cdot \frac{1}{2 \sqrt{x}} \\ \frac{d y}{d x}=y \cdot\left(\frac{1}{\sqrt{x}}+\log (\mathrm{x}) \cdot \frac{1}{2 \sqrt{x}}\right) \\ [/Tex]
Step 5: Substitute back the value of y
[Tex] \frac{d y}{d x}=\mathrm{x}^{\sqrt{x}} \cdot\left(\frac{1}{\sqrt{x}}+\log (\mathrm{x}) \cdot \frac{1}{2 \sqrt{x}}\right) [/Tex]
Logarithmic Differentiation
Logarithmic Differentiation helps to find the derivatives of complicated functions, using the concept of logarithms. Sometimes finding the differentiation of the function is very tough but differentiating the logarithm of the same function is very easy, then in such cases, the logarithmic differentiation formula is used.
In calculus, the differentiation of some complex functions is found first by taking a log and then finding the logarithmic derivative of that function.
In this article, we will learn about Logarithmic Differentiation in detail.
Table of Content
- What is Logarithmic Differentiation?
- Logarithmic Differentiation Formula
- Derivation of Logarithmic Differentiation Formula
- Applications of Log Differentiation
- Product of Functions (Product Rule)
- Division of Functions (Quotient Rule)
- Exponential Functions
- Method to Solve Logarithmic Functions
- Solved Examples on Logarithmic Differentiation
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