\( \newcommand{\abs}[1]{\left| \, {#1} \, \right| } \) \( \newcommand{\cm}{\mathrm{cm} } \) \( \newcommand{\sec}{ \, \mathrm{sec} \, } \) \( \newcommand{\units}[1]{\,\text{#1}} \) \( \newcommand{\vhat}[1]{\,\hat{#1}} \) \( \newcommand{\vhati}{\,\hat{i}} \) \( \newcommand{\vhatj}{\,\hat{j}} \) \( \newcommand{\vhatk}{\,\hat{k}} \) \( \newcommand{\vect}[1]{\boldsymbol{\vec{#1}}} \) \( \newcommand{\norm}[1]{\|{#1}\|} \) \( \newcommand{\arccot}{ \, \mathrm{arccot} \, } \) \( \newcommand{\arcsec}{ \, \mathrm{arcsec} \, } \) \( \newcommand{\arccsc}{ \, \mathrm{arccsc} \, } \) \( \newcommand{\sech}{ \, \mathrm{sech} \, } \) \( \newcommand{\csch}{ \, \mathrm{csch} \, } \) \( \newcommand{\arcsinh}{ \, \mathrm{arcsinh} \, } \) \( \newcommand{\arccosh}{ \, \mathrm{arccosh} \, } \) \( \newcommand{\arctanh}{ \, \mathrm{arctanh} \, } \) \( \newcommand{\arccoth}{ \, \mathrm{arccoth} \, } \) \( \newcommand{\arcsech}{ \, \mathrm{arcsech} \, } \) \( \newcommand{\arccsch}{ \, \mathrm{arccsch} \, } \)

17Calculus - Logarithmic Differentiation

17Calculus
Single Variable Calculus
Derivatives
Integrals
Multi-Variable Calculus
Precalculus
Functions

This topic is usually found in the section discussing implicit differentiation and sometimes instructors do not make a distinction between the two. But logarithmic differentiation is a very specific technique and often uses implicit differentiation along the way.

Recommended Books on Amazon (affiliate links)

Complete 17Calculus Recommended Books List

Prime Student 6-month Trial

There are two main types of equations that you will use logarithmic differentiation on
1. equations where you have a variable in an exponent
2. equations that are quite complicated and can be simplified using logarithms.
In both cases, we introduce logarithms into the equation that may not have been there before, apply some simple rules and then take the derivative. Let's look at each case.

Variables In The Exponent

Remember that you can use the power rule on \(x^2\) but you can't use the power rule on \(2^x\) or \(y^x\).

So, what we do is introduce a natural log into the equation, without changing the problem of course. The goal is to bring the exponent down so that we can take the derivative of it.

These are the rules we use

1. \( \ln(x^y) = y~ \ln(x) \)

2. \( e^{\ln(z)} = z \)

Notice the first rule brings the exponent down in front of the natural log term, in which case, we can use the product rule to take the derivative. The second rule is usually used to reverse the process after taking the derivative.

Let's look at an example. One of the practice problems shows how to calculate the derivative of \( y = x^x \). To do this one, we need to bring the x in the exponent down (since we can't use the power rule). To accomplish this, we take the natural log of both sides, like this:

\(\displaystyle{ \begin{array}{rcl} y & =& x^x \\ \ln(y) & = & \ln(x^x) \\ \ln(y) & = & x \ln(x) \end{array} }\)

Now we can take the derivative of this last equation using chain rule and the product rule. [For a complete solution, see practice problem 890.]

Simplifying

In some cases, we could use the product and/or quotient rules to take a derivative but, using logarithmic differentiation, the derivative would be much easier to find. One of the practice problems is to take the derivative of \(\displaystyle{ y = \frac{(\sin(x))^2(x^3+1)^4}{(x+3)^8} }\). We could use the product and quotient rules here but, if we take the logarithm of both sides, simplify, take the derivative, then convert back, it is much easier. [see practice problem 892 for how to find the derivative \( dy/dx \)]

You Can Have an Amazing Memory: Learn Life-Changing Techniques and Tips from the Memory Maestro

Practice

Unless otherwise instructed, use logarithmic differentiation to calculate the derivative of these functions.

Basic

\( y=5^x \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of \( y=5^x \)

Solution

MathTV - 1543 video solution

video by MathTV

Log in to rate this practice problem and to see it's current rating.

\( y = x^x \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y = x^x \)

Final Answer

\( d[x^x]/dx = x^x(1+\ln(x)) \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y = x^x \)

Solution

\( \ln(y) = \ln(x^x) \)

\( \ln(y) = x \ln(x) \)

\(\displaystyle{ \frac{d}{dx}[\ln(y)] = \frac{d}{dx}[x \ln(x)] }\)

\( (1/y)(dy/dx) = x(1/x) + \ln(x)(1) \)

\( dy/dx = y(1+\ln(x)) \)

\( dy/dx = x^x(1+\ln(x)) \)

Notice we could not use the power rule since the exponent is not a rational number.
Here is a video solution.

blackpenredpen - 890 video solution

video by blackpenredpen

Final Answer

\( d[x^x]/dx = x^x(1+\ln(x)) \)

Log in to rate this practice problem and to see it's current rating.

For \( f(x)=x^{2x} \), determine \(f'(x)\) and \(f'(1)\) using logarithmic differentiation.

Problem Statement

For \( f(x)=x^{2x} \), determine \(f'(x)\) and \(f'(1)\) using logarithmic differentiation. Give your answers in exact, completely factored form.

Solution

MIP4U - 1546 video solution

video by MIP4U

Log in to rate this practice problem and to see it's current rating.

\( y = x^{e^x} \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y = x^{e^x} \)

Final Answer

\( dy/dx=x^{e^x-1}e^x(1+x\ln(x)) \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y = x^{e^x} \)

Solution

Notice we cannot use the power rule since the exponent, \(e^x\), is not a rational number. So to get the factor out of the exponent, we use logarithms.

\( \ln(y) = \ln(x^{e^x}) \)

\( \ln(y) = e^x \ln(x) \)

\(\displaystyle{ \frac{1}{y} \cdot \frac{dy}{dx} = e^x (1/x) + \ln(x) e^x }\)

\(\displaystyle{ \frac{dy}{dx} = ye^x(1/x+\ln(x)) }\)

\(\displaystyle{ \frac{dy}{dx} = \frac{ye^x}{x}(1+x \ln(x)) }\)

\(\displaystyle{ \frac{dy}{dx} = \frac{x^{e^x}e^x}{x}(1+x \ln(x)) }\)

\(\displaystyle{ \frac{dy}{dx} = x^{e^x-1}e^x(1+x \ln(x)) }\)

Final Answer

\( dy/dx=x^{e^x-1}e^x(1+x\ln(x)) \)

Log in to rate this practice problem and to see it's current rating.

\( y=(\ln x)^x \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y=(\ln x)^x \)

Solution

PatrickJMT - 894 video solution

video by PatrickJMT

Log in to rate this practice problem and to see it's current rating.

\( y = x^{\sin(x)} \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y = x^{\sin(x)} \)

Solution

MathTV - 1544 video solution

video by MathTV

Log in to rate this practice problem and to see it's current rating.

\(y=(x^2)^{\sin(x)}\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(y=(x^2)^{\sin(x)}\)

Solution

PatrickJMT - 895 video solution

video by PatrickJMT

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{y=\frac{(x+2)^2}{\sqrt{x^2+1}}}\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{y=\frac{(x+2)^2}{\sqrt{x^2+1}}}\)

Solution

MIP4U - 1545 video solution

video by MIP4U

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{y=\frac{x^4\sqrt{x-3}}{(x+1)^3}}\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{y=\frac{x^4\sqrt{x-3}}{(x+1)^3}}\)

Solution

MIP4U - 1548 video solution

video by MIP4U

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{ y = \sqrt{\frac{1-x}{1+x}} }\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{ y = \sqrt{\frac{1-x}{1+x}} }\)

Solution

Houston Math Prep - 1550 video solution

Log in to rate this practice problem and to see it's current rating.

\( y=x^{x^2} \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y=x^{x^2} \)

Solution

Houston Math Prep - 1552 video solution

Log in to rate this practice problem and to see it's current rating.

\( y = (\sin(x))^x \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y = (\sin(x))^x \)

Solution

TheInfiniteLooper - 1553 video solution

Log in to rate this practice problem and to see it's current rating.

\( y = (\cos x)^{\tan x} \)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \( y = (\cos x)^{\tan x} \)

Solution

TheInfiniteLooper - 1554 video solution

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{ y=\frac{2(x^2+1)}{\sqrt{\cos(2x)}} }\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{ y=\frac{2(x^2+1)}{\sqrt{\cos(2x)}} }\)

Final Answer

\(\displaystyle{ \frac{dy}{dx} = \left[ \frac{2x}{x^2+1} + \tan(2x) \right] \frac{2(x^2+1)}{\sqrt{\cos(2x)}} }\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{ y=\frac{2(x^2+1)}{\sqrt{\cos(2x)}} }\)

Solution

There is a mistake in this video. When he first takes the derivative, he drops a factor of two from the first term on the right side of the equal sign. Actually, I would do one more simplification than he does before taking the derivative by expanding \(\ln [2(x^2+1)] = \ln 2 + \ln(x^2+1)\). Then when you take the derivative of \(\ln 2\) you get zero.

SchoolOfChuck - 1555 video solution

video by SchoolOfChuck

Final Answer

\(\displaystyle{ \frac{dy}{dx} = \left[ \frac{2x}{x^2+1} + \tan(2x) \right] \frac{2(x^2+1)}{\sqrt{\cos(2x)}} }\)

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{ y=(\sin \theta)^{\sqrt{\theta}} }\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \( dy/d\theta \) of the function \(\displaystyle{ y=(\sin \theta)^{\sqrt{\theta}} }\)

Solution

SchoolOfChuck - 1556 video solution

video by SchoolOfChuck

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{ f(x)=(2x-3)^2(5x^2+2)^3 }\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{ f(x)=(2x-3)^2(5x^2+2)^3 }\)

Solution

MIP4U - 1549 video solution

video by MIP4U

Log in to rate this practice problem and to see it's current rating.

Intermediate

Find all values of \(x\) for which the curve \( y = (x^2/4)^x \) has horizontal tangents.

Problem Statement

Find all values of \(x\) for which the curve \( y = (x^2/4)^x \) has horizontal tangents.

Final Answer

\( x = \pm 2/e \)

Problem Statement

Find all values of \(x\) for which the curve \( y = (x^2/4)^x \) has horizontal tangents.

Solution

\(\displaystyle{ y = (x^2/4)^x }\)

\(\displaystyle{ \ln(y) = \ln[ (x^2/4)^x ] }\)

\(\displaystyle{ \ln(y) = x\ln(x^2/4) }\)

\(\displaystyle{ \ln(y) = x[ \ln x^2 - \ln 4] }\)

\(\displaystyle{ \ln(y) = x[ 2\ln x - \ln 4] }\)

\(\displaystyle{ \ln(y) = [ 2x\ln x - x\ln 4] }\)

\(\displaystyle{ \frac{d}{dx}[\ln(y)] = \frac{d}{dx}[ 2x\ln x - x\ln 4] }\)

\(\displaystyle{ \frac{1}{y}\frac{dy}{dx} = (2x)(1/x) + 2\ln(x) - \ln 4 }\)

\(\displaystyle{ \frac{dy}{dx} = y[ 2 + \ln(x^2/4) ] }\)

\(\displaystyle{ \frac{dy}{dx} = (x^2/4)^x [ 2 + \ln(x^2/4) ] }\)

Plotting the \( y = (x^2/4)^x \), which is the first term on the right of the equal sign, we can see that this function is never equal to zero. Using the zero-product rule, we can solve for \(x\) in the second term.

\(\displaystyle{ 2 + \ln(x^2/4) = 0 }\)

\(\displaystyle{ \ln(x^2/4) = -2 }\)

\(\displaystyle{ x^2/4 = e^{-2} }\)

\(\displaystyle{ x^2 = 4e^{-2} }\)

\(\displaystyle{ x = \pm 2/e }\)

Although not asked to in the problem statement, we decided to plot the original function and check our answers.

Final Answer

\( x = \pm 2/e \)

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{y=\frac{(\sin(x))^2(x^3+1)^4}{(x+3)^8}}\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{y=\frac{(\sin(x))^2(x^3+1)^4}{(x+3)^8}}\)

Solution

PatrickJMT - 892 video solution

video by PatrickJMT

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{ y=\sqrt{x}e^{x^2}(x^2+1)^{10} }\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{ y=\sqrt{x}e^{x^2}(x^2+1)^{10} }\)

Solution

PatrickJMT - 893 video solution

video by PatrickJMT

Log in to rate this practice problem and to see it's current rating.

For \(\displaystyle{f(x)=\frac{x^2(x+2)^4}{(2x^2-1)^3}}\), find \(f'(x)\) and \(f'(4)\) using logarithmic differentiation.

Problem Statement

For \(\displaystyle{f(x)=\frac{x^2(x+2)^4}{(2x^2-1)^3}}\), find \(f'(x)\) and \(f'(4)\) using logarithmic differentiation. Give your answers in exact, completely factored form.

Solution

MIP4U - 1547 video solution

video by MIP4U

Log in to rate this practice problem and to see it's current rating.

\(\displaystyle{y=\sqrt[3]{\frac{x(x^2+1)^4}{x^3-2}}}\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{y=\sqrt[3]{\frac{x(x^2+1)^4}{x^3-2}}}\)

Solution

Houston Math Prep - 1551 video solution

Log in to rate this practice problem and to see it's current rating.

Advanced

\(\displaystyle{y=x^{(x^x)}}\)

Problem Statement

Use logarithmic differentiation to calculate the derivative \(dy/dx\) of the function \(\displaystyle{y=x^{(x^x)}}\)

Solution

Khan Academy - 896 video solution

video by Khan Academy

Log in to rate this practice problem and to see it's current rating.

Really UNDERSTAND Calculus

Log in to rate this page and to see it's current rating.

To bookmark this page and practice problems, log in to your account or set up a free account.

Search Practice Problems

Do you have a practice problem number but do not know on which page it is found? If so, enter the number below and click 'page' to go to the page on which it is found or click 'practice' to be taken to the practice problem.

math and science learning techniques

Shop Amazon - Rent Textbooks - Save up to 80%

As an Amazon Associate I earn from qualifying purchases.

I recently started a Patreon account to help defray the expenses associated with this site. To keep this site free, please consider supporting me.

Support 17Calculus on Patreon

Variables In The Exponent

Simplifying

Practice

Practice Search

Page Sections

Practice Instructions

Unless otherwise instructed, use logarithmic differentiation to calculate the derivative of these functions.

Do NOT follow this link or you will be banned from the site!

When using the material on this site, check with your instructor to see what they require. Their requirements come first, so make sure your notation and work follow their specifications.

DISCLAIMER - 17Calculus owners and contributors are not responsible for how the material, videos, practice problems, exams, links or anything on this site are used or how they affect the grades or projects of any individual or organization. We have worked, to the best of our ability, to ensure accurate and correct information on each page and solutions to practice problems and exams. However, we do not guarantee 100% accuracy. It is each individual's responsibility to verify correctness and to determine what different instructors and organizations expect. How each person chooses to use the material on this site is up to that person as well as the responsibility for how it impacts grades, projects and understanding of calculus, math or any other subject. In short, use this site wisely by questioning and verifying everything. If you see something that is incorrect, contact us right away so that we can correct it.

Links and banners on this page are affiliate links. We carefully choose only the affiliates that we think will help you learn. Clicking on them and making purchases help you support 17Calculus at no extra charge to you. However, only you can decide what will actually help you learn. So think carefully about what you need and purchase only what you think will help you.

We use cookies on this site to enhance your learning experience.

17calculus

Copyright © 2010-2022 17Calculus, All Rights Reserved     [Privacy Policy]     [Support]     [About]

mathjax.org
Real Time Web Analytics