Derivatives of Exponential and Logarithmic Functions - 3.4 | Chapter 3: Calculus | ICSE Class 12 Mathematics
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Derivatives of Exponential Functions

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Teacher
Teacher

Today, we will start with the derivatives of exponential functions. Let's begin with the natural exponential function, which is \( e^x \). Does anyone know what the derivative of \( e^x \) is?

Student 1
Student 1

I think it's just \( e^x \), right?

Teacher
Teacher

Exactly! The derivative of \( e^x \) is indeed \( e^x \). This means that the rate at which \( e^x \) changes is proportional to its current value, which is a unique property of the exponential function.

Student 2
Student 2

What about other bases? Is there a formula for that?

Teacher
Teacher

Great question! For an exponential function with a different base, say \( a^x \), the derivative is given by \( \frac{d}{dx}[a^x] = a^x \ln(a) \). So, if you know the base, you can easily compute the derivative!

Student 3
Student 3

Can you give an example with a specific base?

Teacher
Teacher

Sure! Let’s take \( f(x) = 2^x \). The derivative would be \( \frac{d}{dx}[2^x] = 2^x \ln(2) \).

Student 4
Student 4

So, if we substitute a value like \( x = 1 \), would it help us find the rate of change?

Teacher
Teacher

Exactly! If you plug in \( x = 1 \), you'd get \( 2^1 \ln(2) \), which gives you the instantaneous rate of change at that point.

Derivatives of Logarithmic Functions

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Teacher
Teacher

Now, let’s transition to logarithmic functions. Who can tell me the derivative of \( \ln(x) \)?

Student 1
Student 1

I believe it's \( \frac{1}{x} \).

Teacher
Teacher

Correct! The derivative of \( \ln(x) \) is \( \frac{1}{x} \). This explains how the natural logarithm grows slower than polynomial functions.

Student 2
Student 2

What about logarithms with different bases?

Teacher
Teacher

For logarithms to any base, such as \( \log_a(x) \), the derivative is given by \( \frac{1}{x \, \ln(a)} \). This means that the growth rate depends on both the input value and the logarithmic base.

Student 3
Student 3

Could you show a practical application for finding the derivative of a logarithm?

Teacher
Teacher

Certainly! In real-life situations, such as calculating pH in chemistry, we often use logarithmic functions where understanding the rate of change is crucial. For instance, if we're dealing with \( \log_{10}(x) \), we'd apply the formula \( \frac{1}{x \, ext{ln}(10)} \).

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section focuses on the derivatives of exponential and logarithmic functions, which are vital for calculus applications.

Standard

In this section, we explore how to differentiate exponential functions such as e^x and a^x, along with logarithmic functions including ln(x) and log_a(x). Understanding these derivatives is foundational for advanced calculus concepts and real-world applications.

Detailed

Detailed Summary

This section delves into the derivatives of exponential and logarithmic functions, key components of calculus that are crucial for various applications in mathematics, physics, engineering, and economics. Understanding how to differentiate these functions allows for deeper insights into how they change over time.

Key Points Covered:

  1. Exponential Functions:
  2. The derivative of the exponential function, specifically the natural exponential function, is given by:
    • If \( f(x) = e^x \), then \( \frac{d}{dx}[e^x] = e^x \).
  3. For other bases, \( f(x) = a^x \) (where \( a \) is a constant), the derivative is:
    • \( \frac{d}{dx}[a^x] = a^x \ln(a) \).
  4. Logarithmic Functions:
  5. The derivative for the natural logarithmic function is crucial:
    • If \( f(x) = \ln(x) \), then \( \frac{d}{dx}[\ln(x)] = \frac{1}{x} \).
  6. For the logarithm to any base \( a \), the derivative is expressed as:
    • If \( f(x) = \log_a(x) \), then \( \frac{d}{dx}[\log_a(x)] = \frac{1}{x\ln(a)} \).

These derivatives form the foundation for many applications in higher-level calculus and real-world scenarios where exponential growth and decay or logarithmic measures are relevant.

Audio Book

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Derivatives of Exponential Functions

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  1. Exponential Functions:
    If 𝑓(π‘₯) = 𝑒π‘₯, then
    𝑑 [𝑒π‘₯] = 𝑒π‘₯
    𝑑π‘₯
    More generally, if 𝑓(π‘₯) = π‘Žπ‘₯ (where π‘Ž is a constant), then
    𝑑 [π‘Žπ‘₯] = π‘Žπ‘₯ln(π‘Ž)
    𝑑π‘₯

Detailed Explanation

This chunk introduces derivatives of exponential functions. The first formula states that if the function f(x) equals e raised to the power of x, then the derivative of this function is simply e raised to the power of x. This is a unique property of the mathematical constant 'e'. For any exponential function where a is a constant (like 2, 10, etc.), the derivative is given by multiplying the function itself, ax, by the natural logarithm of a (ln(a)). Essentially, we are finding how quickly this function grows with respect to x.

Examples & Analogies

Think of investing money in a bank that offers compound interest, which grows exponentially. If you invest an amount, say $1000, it might grow as 1000e^x, where x represents time. The derivative tells you how fast your investment is growing at any moment. If you are looking at your account balance daily, the 'rate of change' of your balance represents the bank's growth contribution, and understanding this helps you make informed financial decisions.

Derivatives of Logarithmic Functions

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  1. Logarithmic Functions:
    If 𝑓(π‘₯) = ln(π‘₯), then
    𝑑 1
    [ln(π‘₯)] =
    𝑑π‘₯ π‘₯
    If 𝑓(π‘₯) = log_a(π‘₯), then
    𝑑 1
    [log_a(π‘₯)] =
    𝑑π‘₯ π‘₯ln(π‘Ž)

Detailed Explanation

This chunk discusses the derivatives of logarithmic functions. If the function f(x) is the natural logarithm of x (ln(x)), its derivative is the reciprocal of x. This means as x increases, the rate of change of ln(x) decreases. For logarithms with a different base (a), the derivative is also the reciprocal of x, but multiplied by the natural logarithm of the base (ln(a)). This property is useful when transforming or rewriting functions in calculus.

Examples & Analogies

Consider the process of measuring sound intensity. You often use a decibel scale, which is logarithmic; small changes in the sound’s power level are compared to a baseline intensity. When teaching someone about how sound levels change, you can explain that while our perception adjusts logarithmically, the derivative gives us the exact rate at which our understanding of sound power changes at a given level. This helps us to quantify differences in sound terms that are more intuitive to ear and less linked to raw power which might be harder to grasp.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Exponential Derivative: The derivative of \( e^x \) is \( e^x \).

  • General Exponential Derivative: For \( a^x \), the derivative is \( a^x \ln(a) \).

  • Natural Logarithm Derivative: The derivative of \( \ln(x) \) is \( \frac{1}{x} \).

  • Logarithmic Derivative: For \( log_a(x) \), the derivative is \( \frac{1}{x \, ext{ln}(a)} \).

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example 1: Differentiate \( f(x) = 3^x \). The derivative is \( f'(x) = 3^x \ln(3) \).

  • Example 2: Differentiate \( g(x) = \ln(5x) \). The derivative is \( g'(x) = \frac{5}{5x} = \frac{1}{x}. \)

  • Example 3: Find the derivative of \( h(x) = 2^x + 3^x \). The derivative is \( h'(x) = 2^x \ln(2) + 3^x \ln(3) \).

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎡 Rhymes Time

  • For e to the x, just take a hack, the same you get right back on track!

🎯 Super Acronyms

E.L.L. - Exponential, Logarithmic, Linear derivatives.

🧠 Other Memory Gems

  • For a derivative of a base a, remember the form: a^x ln(a)! This works any day.

πŸ“– Fascinating Stories

  • Imagine a plant growing exponentially; as time goes by, its growth rate matches its height, that's e^x. For a logarithm, it's like counting levels on a ladder, every step is slower, reflecting 1/x as you climb higher.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Exponential Function

    Definition:

    A mathematical function of the form f(x) = a^x, where a is a positive constant.

  • Term: Natural Exponential Function

    Definition:

    The exponential function with base e, denoted as f(x) = e^x.

  • Term: Derivative

    Definition:

    A measure of how a function changes as its input changes.

  • Term: Logarithmic Function

    Definition:

    A function of the form f(x) = log_a(x), which is the inverse of the exponential function.

  • Term: Natural Logarithm

    Definition:

    The logarithm with base e, denoted as ln(x).