Chapter 6: Problem 14
Find the indefinite integral. $$ \int \frac{x}{\sqrt[5]{2 x^{2}+5}} d x $$
Short Answer
Expert verified
\( \frac{5}{16} (2x^2 + 5)^{4/5} + C \)
Step by step solution
01
Identify the Substitution
To solve the integral \( \int \frac{x}{\sqrt[5]{2x^2+5}}\, dx \), we need to make a substitution that simplifies the integrand. Notice that \( 2x^2 + 5 \) is under a root, so let \( u = 2x^2 + 5 \). This substitution will help manage the complexity of the root.
02
Differentiate the Substitution
Differentiate the substitution \( u = 2x^2 + 5 \) with respect to \( x \) to find \( \frac{du}{dx} \). This gives \( du = 4x\, dx \). We can solve for \( x\, dx \) as \( x\, dx = \frac{1}{4}du \).
03
Rewrite the Integral
Substitute \( u = 2x^2 + 5 \) and \( x\, dx = \frac{1}{4}du \) into the integral: \[ \int \frac{x}{\sqrt[5]{2x^2 + 5}}\, dx = \int \frac{1}{4} \cdot \frac{1}{u^{1/5}}\, du. \] This simplifies to \[ \frac{1}{4} \int u^{-1/5}\, du. \]
04
Integrate
Perform the integration: \( \frac{1}{4} \int u^{-1/5} \, du \). Use the power rule for integration \( \int u^n \, du = \frac{u^{n+1}}{n+1} + C \). Here, \( n = -\frac{1}{5} \). The integral becomes \[ \frac{1}{4} \cdot \frac{u^{4/5}}{4/5} + C = \frac{1}{4} \cdot \frac{5}{4} u^{4/5} + C \] \[ = \frac{5}{16} u^{4/5} + C. \]
05
Substitute Back
Substitute back \( u = 2x^2 + 5 \) into the integrated expression: \[ \frac{5}{16} (2x^2 + 5)^{4/5} + C. \] This gives the final indefinite integral solution.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Substitution Method
The substitution method is a technique used to simplify complex integrals, making them easier to evaluate. It involves substituting a part of the integrand with a new variable—commonly denoted as \( u \). This transformation usually reduces the complexity of the integral, turning it into a more familiar form.To use the substitution method, follow these steps:
- Identify a portion of the integrand that can be replaced by a simpler expression. Look for expressions that appear in the derivative to simplify calculations.
- Make a substitution, such as \( u = g(x) \), where \( g(x) \) is the chosen portion of the integrand.
- Differentiate the substitution to express \( dx \) in terms of \( du \). This can be written as \( du = g'(x)\, dx \), and solve for \( dx \).
- Rewrite the original integral in terms of \( u \) and \( du \) and perform the integration.
- Finally, substitute back the original expression for \( u \) to get the solution in terms of the original variable.
Power Rule for Integration
The power rule for integration is a simple yet powerful technique to find integrals of expressions with powers. When applying the power rule, the integral of \( u^n \) with respect to \( u \) is calculated using the formula:\[ \int u^n \, du = \frac{u^{n+1}}{n+1} + C \]where \( n eq -1 \) and \( C \) is the constant of integration. Here's how it works:
- Add 1 to the exponent \( n \) of the variable \( u \).
- Divide by the new exponent \( n + 1 \).
- Don't forget to add the constant of integration \( C \).
Integration Techniques
Integration techniques are vital for tackling a wide range of functions you may encounter in calculus. Various techniques exist, each suitable for different kinds of problems. Here, we encountered two commonly used techniques: substitution and the power rule. Let's explore them further.
- Substitution Method: Often used for integrals involving composites or nested functions. It simplifies the integral by changing the variable, making awkward expressions easier to handle.
- Power Rule for Integration: A straightforward technique for polynomials. If the integrand is a simple polynomial in standard form, apply the power rule as a first choice.
- Partial Fraction Decomposition: Useful for rational functions, splitting complex fractions into simpler ones before integrating.
- Integration by Parts: Efficient for products of functions. It uses the formula \( \int u \, dv = uv - \int v \, du \) to integrate pieces separately.
- Trigonometric Substitution: Applies primarily to integrals involving square roots and trigonometric identities.