Understanding the Chain Rule

Oct 13, 2025 by wbrum.org 71 views

Introduction

In calculus, the chain rule is a fundamental concept that allows us to differentiate composite functions. Given a composite function $$f(x) = g(h(x))$$, we can find the derivative of $$f(x)$$ using the chain rule. In this article, we will explore how to apply the chain rule to find the derivative of a composite function and then evaluate it at a specific point.

Understanding the Chain Rule

The chain rule is a formula for finding the derivative of a composite function. It states that if we have a composite function $$f(x) = g(h(x))$$, then the derivative of $$f(x)$$ is given by:

f^{\prime}(x) = g^{\prime}(h(x)) \cdot h^{\prime}(x)

This formula tells us that the derivative of the composite function is equal to the derivative of the outer function evaluated at the inner function, multiplied by the derivative of the inner function.

Applying the Chain Rule

To apply the chain rule, we need to find the derivatives of the outer and inner functions. Let's consider an example to illustrate this.

Suppose we have a composite function $$f(x) = g(h(x))$$, where $$g(x) = x^2 + 1$$ and $$h(x) = 2x - 1$$. We want to find the derivative of $$f(x)$$ using the chain rule.

First, we need to find the derivatives of the outer and inner functions. The derivative of $$g(x)$$ is:

g^{\prime}(x) = 2x

The derivative of $$h(x)$$ is:

h^{\prime}(x) = 2

Now, we can apply the chain rule to find the derivative of $$f(x)$$:

f^{\prime}(x) = g^{\prime}(h(x)) \cdot h^{\prime}(x)

f^{\prime}(x) = 2(h(x)) \cdot 2

f^{\prime}(x) = 4h(x)

Evaluating the Derivative at a Specific Point

Now that we have found the derivative of $$f(x)$$, we can evaluate it at a specific point. Let's say we want to find the value of $$f^{\prime}(3)$$.

To do this, we need to substitute $$x = 3$$ into the derivative of $$f(x)$$:

f^{\prime}(3) = 4h(3)

h(3) = 2(3) - 1

h(3) = 5

f^{\prime}(3) = 4(5)

f^{\prime}(3) = 20

Conclusion

In this article, we have explored how to apply the chain rule to find the derivative of a composite function and then evaluate it at a specific point. We have seen that the chain rule allows us to differentiate composite functions by finding the derivatives of the outer and inner functions and then multiplying them together. We have also seen how to evaluate the derivative of a composite function at a specific point by substituting the value of the point into the derivative.

Frequently Asked Questions

What is the chain rule? The chain rule is a formula for finding the derivative of a composite function.
How do I apply the chain rule? To apply the chain rule, you need to find the derivatives of the outer and inner functions and then multiply them together.
What is the derivative of a composite function? The derivative of a composite function is equal to the derivative of the outer function evaluated at the inner function, multiplied by the derivative of the inner function.

References

[1] Calculus by Michael Spivak
[2] Calculus: A First Course by Michael Sullivan
[3] Calculus: Early Transcendentals by James Stewart

Introduction

In our previous article, we explored how to apply the chain rule to find the derivative of a composite function and then evaluate it at a specific point. In this article, we will answer some frequently asked questions about the chain rule and provide additional examples to help you understand this important concept in calculus.

Q&A

Q: What is the chain rule?

A: The chain rule is a formula for finding the derivative of a composite function. It states that if we have a composite function $$f(x) = g(h(x))$$, then the derivative of $$f(x)$$ is given by:

f^{\prime}(x) = g^{\prime}(h(x)) \cdot h^{\prime}(x)

Q: How do I apply the chain rule?

A: To apply the chain rule, you need to find the derivatives of the outer and inner functions and then multiply them together. For example, if we have a composite function $$f(x) = g(h(x))$$, where $$g(x) = x^2 + 1$$ and $$h(x) = 2x - 1$$, we can find the derivative of $$f(x)$$ using the chain rule as follows:

f^{\prime}(x) = g^{\prime}(h(x)) \cdot h^{\prime}(x)

f^{\prime}(x) = 2(h(x)) \cdot 2

f^{\prime}(x) = 4h(x)

Q: What is the derivative of a composite function?

A: The derivative of a composite function is equal to the derivative of the outer function evaluated at the inner function, multiplied by the derivative of the inner function. For example, if we have a composite function $$f(x) = g(h(x))$$, where $$g(x) = x^2 + 1$$ and $$h(x) = 2x - 1$$, the derivative of $$f(x)$$ is:

f^{\prime}(x) = g^{\prime}(h(x)) \cdot h^{\prime}(x)

f^{\prime}(x) = 2(h(x)) \cdot 2

f^{\prime}(x) = 4h(x)

Q: How do I evaluate the derivative of a composite function at a specific point?

A: To evaluate the derivative of a composite function at a specific point, you need to substitute the value of the point into the derivative. For example, if we have a composite function $$f(x) = g(h(x))$$, where $$g(x) = x^2 + 1$$ and $$h(x) = 2x - 1$$, and we want to find the value of $$f^{\prime}(3)$$, we can substitute $$x = 3$$ into the derivative of $$f(x)$$ as follows:

f^{\prime}(3) = 4h(3)

h(3) = 2(3) - 1

h(3) = 5

f^{\prime}(3) = 4(5)

f^{\prime}(3) = 20

Q: What are some common mistakes to avoid when applying the chain rule?

A: Some common mistakes to avoid when applying the chain rule include:

Forgetting to find the derivatives of the outer and inner functions
Not multiplying the derivatives together correctly
Not substituting the value of the point into the derivative correctly

Additional Examples

Example 1

Suppose we have a composite function $$f(x) = g(h(x))$$, where $$g(x) = x^3 + 2$$ and $$h(x) = x^2 - 1$$. Find the derivative of $$f(x)$$ using the chain rule.

Solution:

f^{\prime}(x) = g^{\prime}(h(x)) \cdot h^{\prime}(x)

f^{\prime}(x) = 3(h(x))^2 \cdot 2x

f^{\prime}(x) = 6x(h(x))^2

Example 2

Suppose we have a composite function $$f(x) = g(h(x))$$, where $$g(x) = x^2 + 1$$ and $$h(x) = 2x - 1$$. Find the value of $$f^{\prime}(3)$$.

Solution:

f^{\prime}(3) = 4h(3)

h(3) = 2(3) - 1

h(3) = 5

f^{\prime}(3) = 4(5)

f^{\prime}(3) = 20

Conclusion

In this article, we have answered some frequently asked questions about the chain rule and provided additional examples to help you understand this important concept in calculus. We have seen that the chain rule allows us to differentiate composite functions by finding the derivatives of the outer and inner functions and then multiplying them together. We have also seen how to evaluate the derivative of a composite function at a specific point by substituting the value of the point into the derivative.

Frequently Asked Questions

What is the chain rule?
How do I apply the chain rule?
What is the derivative of a composite function?
How do I evaluate the derivative of a composite function at a specific point?
What are some common mistakes to avoid when applying the chain rule?

References

[1] Calculus by Michael Spivak
[2] Calculus: A First Course by Michael Sullivan
[3] Calculus: Early Transcendentals by James Stewart