Calculus Lesson 2 - Chain Rule

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Questions and Answers

Given $f(x) = \sin(x)$ and $g(x) = 3x$, what is the composite function $f(g(x))$?

  • $3x + \sin(x)$
  • $\sin(x) \cdot 3x$
  • $\sin(3x)$ (correct)
  • $3\sin(x)$

If $y = \csc^2(2x - \pi)$, which of the following correctly identifies the outer function $f(x)$ and the inner function $g(x)$ in the composition $f(g(x))$?

  • $f(x) = x^2$, $g(x) = \csc(2x - \pi)$
  • $f(x) = 2x - \pi$, $g(x) = \csc^2(x)$
  • $f(x) = \csc^2(x)$, $g(x) = 2x - \pi$ (correct)
  • $f(x) = \csc(x)$, $g(x) = 2x - \pi$

If $y = f(u)$ and $u = g(x)$, and both functions are differentiable, the chain rule states:

  • $\frac{dy}{dx} = \frac{dx}{dy} \cdot \frac{du}{dx}$
  • $\frac{dy}{dx} = \frac{dy}{du} + \frac{du}{dx}$
  • $\frac{dy}{dx} = \frac{dy}{du} \cdot \frac{du}{dx}$ (correct)
  • $\frac{dy}{dx} = \frac{du}{dx} \cdot \frac{dx}{dy}$

To apply the chain rule to a composite function $f(u(x))$, what is the correct order of steps?

<p>Decompose the function, find $f'(u)$ and $u'(x)$, multiply the resultant derivatives, and substitute back for $u$. (A)</p> Signup and view all the answers

Given $y = 3\sqrt{x^3} - 4x$, find its derivative. Assume $f(x) = 3\sqrt{x}$ and $g(x) = x^3 - 4x$.

<p>$\frac{dy}{dx} = \frac{9x}{2\sqrt{x}} - 4$ (B)</p> Signup and view all the answers

If $y = u^3 - 3u^2 + 1$ and $u = x^2 + 2$, find $\frac{dy}{dx}$.

<p>$\frac{dy}{dx} = 6x^5 + 12x^3$ (A)</p> Signup and view all the answers

Given $f(x) = \sin(3x^2 + 5x - 7)$, find $f'(x)$.

<p>$f'(x) = (6x + 5) \cdot \cos(3x^2 + 5x - 7)$ (C)</p> Signup and view all the answers

If $F(x) = \sqrt{x^2 + 1}$, determine $F'(x)$.

<p>$F'(x) = \frac{x}{\sqrt{x^2 + 1}}$ (A)</p> Signup and view all the answers

What is the primary goal of using u-substitution in integration?

<p>To simplify the integrand into a more manageable form for integration. (D)</p> Signup and view all the answers

What is the first step in applying the substitution rule for integration?

<p>Choose a suitable substitution $u = g(x)$ and find $du = g'(x) dx$. (C)</p> Signup and view all the answers

Evaluate the indefinite integral: $\int (x + 4)^5 dx$.

<p>$\frac{(x + 4)^6}{6} + C$ (A)</p> Signup and view all the answers

Evaluate the integral $\int (x^5 + 2)^9 \cdot 5x^4 dx$.

<p>$\frac{(x^5 + 2)^{10}}{10} + C$ (B)</p> Signup and view all the answers

Determine the integral $\int \frac{z^2}{\sqrt{1 + z^3}} dz$.

<p>$\frac{2}{3} (1 + z^3)^{\frac{1}{2}} + C$ (C)</p> Signup and view all the answers

Compute $\int \frac{x}{\sqrt{x^2 - 1}} dx$.

<p>$\sqrt{x^2 - 1} + C$ (B)</p> Signup and view all the answers

What is the result of the integral $\int \frac{x^3}{\sqrt{x^3 + 5}} dx$?

<p>$\frac{2}{3}(x^3 + 5)^{\frac{3}{2}} - 10(x^3 + 5)^{\frac{1}{2}} + C$ (D)</p> Signup and view all the answers

Using the table of integrals, determine the antiderivative of the function $f(x) = \sec(x)$.

<p>$\ln |\sec(x) + \tan(x)| + C$ (B)</p> Signup and view all the answers

Using the table of integrals, evaluate $\int \frac{dx}{\sqrt{a^2 - x^2}}$.

<p>$\sin^{-1}(\frac{x}{a}) + C$ (A)</p> Signup and view all the answers

Using the table of integrals, find the integral of $\int \csc(x)\cot(x) dx$

<p>$-\csc(x) + C$ (C)</p> Signup and view all the answers

Using the table of integrals, which of the following is the correct formula for $\int \tan(x) dx$?

<p>$-\ln |\cos(x)| + C$ (A)</p> Signup and view all the answers

According to the provided content, which of the following integrals requires a substitution to solve effectively?

<p>$\int (x+4)^5 dx$ (A)</p> Signup and view all the answers

Given the integral $\int f(g(x)) \cdot g'(x) dx$, what does this expression simplify to after applying u-substitution?

<p>$F(u) + C$ (C)</p> Signup and view all the answers

Flashcards

What is the Chain Rule?

A rule for differentiating composite functions. It states that the derivative of f(g(x)) is f'(g(x)) * g'(x).

What is Composition of Functions?

Combining two functions where the output of one function becomes the input of the other, denoted as f(g(x)).

What is u-Substitution?

A technique used to find the antiderivative of a composite function by reversing the chain rule.

What is an Integral?

A formula or method used to find the antiderivative of a function.

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Antidifferentiation by Substitution

A technique that reverses the chain rule, simplifying integration by substituting part of the integrand with a new variable, 'u'.

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How do you perform u-substitution?

When evaluating ∫f(g(x))⋅g'(x) dx, set u = g(x) so the integral becomes ∫f(u) du.

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In ∫(x + 4)⁵ dx, how do you choose 'u'?

Reduce complexity by setting u = x + 4, transforming ∫(x + 4)⁵ dx into ∫u⁵ du.

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How to simplify ∫ (x⁵ + 2)⁹ 5x⁴ dx?

Transform the integral into ∫ u^9 du where u = x⁵ + 2.

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How to solve integrals with substitution?

First, identify a suitable 'u' (e.g., u = 1 + z³) and express the original integral in terms of 'u' before integrating.

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What's the final step in u-substitution?

After u-substitution, remember to express the final answer in terms of the original variable (x).

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Study Notes

  • This material covers Lesson 2 of basic calculus, focusing on the fourth quarter.
  • It discuses antidifferentiation by substitution and using a table of integrals.

Review Lesson: The Chain Rule for Differentiation

  • The chain rule is a method for differentiating composite functions, i.e., functions composed of other functions.

Example 1

  • Find f(g(x)) if f(x) = tan(x) and g(x) = 3x + 2
  • The result is tan(3x + 2)

Example 2: Decomposition of Functions

  • Given a composite function f(g(x)), decomposition involves identifying the outer function f(x) and the inner function g(x).
  • y = 3√(x³-4x): f(x) = 3√x, g(x) = x³ - 4x
  • y = 1/(2x-3)³: f(x) = 1/x³, g(x) = 2x - 3
  • y = sin(3x): f(x) = sin(x), g(x) = 3x
  • y = (3x-8)⁴: f(x) = x⁴, g(x) = 3x - 8
  • y = csc²(2x - π): f(x) = csc²(x), g(x) = 2x - π

The Chain Rule

  • If y = f(u) is a differentiable function of u, and u = g(x) is a differentiable function of x, then y = f(g(x)) is a differentiable function of x.
  • The chain rule is expressed as dy/dx = (dy/du) * (du/dx).
  • An alternative notation is f'(u) = f'(u) * u'.
  • A further notation is d/dx [f(g(x))] = f'(g(x)) * g'(x)

Instructions for the Chain Rule

  • To find the derivative f' of a composite function f(u(x)):
  • Decompose the function into its outer function f(u) and inner function u(x).
  • Differentiate the "mother" function: Find f'(u).
  • Differentiate the composed function: Find u'(x).
  • Multiply the resultant derivatives: f'(x) = f'(u) * u'(x).
  • Substitute for u and simplify the expression.

Chain Rule Derivative Examples

  • Find the derivatives of the following functions:
  • y = 3√(x³-4x): f(x) = 3√x, g(x) = x³ - 4x
  • y = 1/(2x-3)³: f(x) = 1/x³, g(x) = 2x - 3
  • y = (3x-8)⁴: f(x) = x⁴, g(x) = 3x - 8

Example 1

  • Find dy/dx if y = u³ - 3u² + 1 and u = x² + 2:
  • Define f(u) = u³ - 3u² + 1 and u = x² + 2.
  • Find the derivatives: f'(u) = 3u² - 6u and u' = 2x.
  • Apply the chain rule: dy/dx = f'(u) * u' = (3u² - 6u)(2x).
  • Substitute and simplify: dy/dx = 6x⁵ + 12x³.

Example 2

  • Differentiate f(x) = sin(3x² + 5x - 7):
  • Define f(u) = sin(u) and u = 3x² + 5x - 7.
  • Find the derivatives: f'(u) = cos(u) and u' = 6x + 5.
  • Apply the chain rule: f'(x) = f'(u) * u' = cos(u)(6x + 5).
  • Substitute and simplify: f'(x) = (6x + 5)cos(3x² + 5x - 7).

Example 3

  • Find F'(x) if F(x) = √(x² + 1):
  • Define f(u) = √u = u^(1/2) and u = x² + 1.
  • Find the derivatives: f'(u) = (1/2)u^(-1/2) and u' = 2x.
  • Apply the chain rule and simplify: F'(x) = x / √(x² + 1).

Lesson Proper: Antiderivatives via Substitution

  • Compute the antiderivative of a function using substitution rule.
  • Composite functions are functions combined to make a single one.
  • The combination of functions f and g is (f ∘ g)(x) = f(g(x)).
  • To apply the Chain Rule on composite functions, find the derivative of the outer function and multiplying it by the derivative of the inner function.
  • Symbolically: d/dx [f(g(x))] = f'(g(x)) * g'(x), where f'(g(x)) is the derivative of the outside function and g'(x) is the derivative of the inside function.
  • Anti-differentiation by substitution is the inverse of the Chain Rule.
  • ∫f(g(x)) * g'(x) dx can be transformed into ∫F(u) + C = ∫f(u) du.

Example 1

  • Evaluate ∫(x + 4)⁵ dx:
  • Substitute u = x + 4 (du = dx) to simplify the integral to ∫u⁵ du.
  • Evaluate ∫u⁵ du as (u⁶)/6 + C.
  • Substitute x + 4 back in for u, yielding (x + 4)⁶/6 + C.

Example 2

  • Evaluate ∫(x⁵ + 2)⁹ * 5x⁴ dx:
  • Substitute u = x⁵ + 2 (du = 5x⁴ dx) to get ∫u⁹ du.
  • Evaluate ∫u⁹ du as u¹⁰/10 + C.
  • Substitute x⁵ + 2 back in for u, gettting (x⁵ + 2)¹⁰/10 + C.

Example 3

  • Evaluate ∫z² / √(1 + z³) dz:
  • Substitute u = 1 + z³ (du = 3z² dz, z² dz = (1/3) du) to get (1/3) ∫1/√u du.
  • Rewrite as (1/3) ∫u^(-1/2) du, and solve: (2/3)(1 + z³)^(1/2) + C.

Example 4

  • Evaluate ∫x / √(x² - 1) dx:
  • Substitute u = x² - 1 (du = 2x dx, x dx = (1/2) du). The integral becomes ∫(1/2) / √u du.
  • Rewrite as (1/2) ∫u^(-1/2) du and solve to get: (x² - 1)^(1/2) + C.

Example 5

  • Evaluate ∫x³ / √(x³ + 5) dx:
  • Substitute u = x³ + 5 (x³ = u - 5, du = 3x² dx), transforming the integral.
  • Evaluate ∫(u - 5) / √u du to get (2/3)(x³ + 5)^(3/2) - 10(x³ + 5)^(1/2) + C.

Summary Table of Integrals

  • Provides a list of common integrals, useful for solving antidifferentiation problems.
  • Includes integrals of basic functions like xⁿ, eˣ, aˣ, sin x, cos x, and sec²x, as well as trigonometric functions.

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