Chapter 5: Problem 398
In the following exercises, find each indefinite integral, using appropriate substitutions. $$\int \frac{d x}{\sqrt{1-16 x^{2}}}$$
Short Answer
Expert verified
\( \int \frac{d x}{\sqrt{1-16 x^{2}}} = \frac{1}{4} \arcsin(4x) + C \)
Step by step solution
01
Recognize Structure for Trigonometric Substitution
The integrand has the form \( \frac{1}{\sqrt{1 - 16x^2}} \), which suggests using the trigonometric substitution \( x = \frac{1}{4} \sin(\theta) \). This is because \( 1 - 16x^2 \) relates to the identity \( 1 - \sin^2(\theta) = \cos^2(\theta) \).
02
Apply Substitution
Substitute \( x = \frac{1}{4} \sin(\theta) \) into the integrand, thus \( dx = \frac{1}{4} \cos(\theta) d\theta \). Replace in the integral which becomes:\[\int \frac{\frac{1}{4} \cos(\theta) d\theta}{\sqrt{1 - 16(\frac{1}{4} \sin(\theta))^2 }} = \int \frac{\frac{1}{4} \cos(\theta) d\theta}{\sqrt{1 - \sin^2(\theta)}}\]
03
Simplify the Integral
Recognize that \( \sqrt{1 - \sin^2(\theta)} = \cos(\theta) \). Hence, the integrand simplifies:\[\int \frac{\frac{1}{4} \cos(\theta) d\theta}{\cos(\theta)} = \int \frac{1}{4} d\theta\]
04
Integrate with Respect to Theta
Integrate \( \int \frac{1}{4} d\theta = \frac{1}{4} \theta + C \), where \( C \) is the constant of integration.
05
Back-Substitute to Original Variable
Recall that \( x = \frac{1}{4} \sin(\theta) \) implies \( \theta = \arcsin(4x) \). Substitute back to get the integral in terms of \( x \):\[\frac{1}{4} \theta + C = \frac{1}{4} \arcsin(4x) + C\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Trigonometric Substitution
Trigonometric substitution is a powerful technique used in integral calculus, especially for integrals involving square roots. The idea is to simplify the integrand by substituting a trigonometric function for the variable. In this example, the integral \( \int \frac{d x}{\sqrt{1-16 x^{2}}} \) suggests a trigonometric substitution because the expression under the square root resembles the Pythagorean identity \( 1 - \sin^2(\theta) = \cos^2(\theta) \).
- We set \( x = \frac{1}{4} \sin(\theta) \), transforming \( dx = \frac{1}{4} \cos(\theta) d\theta \).
- This substitution leverages the identity \( 1 - 16x^2 \rightarrow 1 - \sin^2(\theta) \), which simplifies to \( \cos^2(\theta) \).
Integral Calculus
Integral calculus is the branch of mathematics concerned with finding antiderivatives or integrals. Indefinite integrals, represented by \( \int f(x) \, dx \), find a function whose derivative is the integrand. In this exercise, our task was to integrate \( \int \frac{d x}{\sqrt{1-16 x^{2}}} \), a classic example for utilizing advanced techniques.
- The primary goal is to remove the challenging square root in the denominator by a suitable substitution.
- After choosing the right trigonometric substitution, the integral simplifies greatly, enabling ease of integration.
Substitution Method
The substitution method in calculus is essential for transforming an integral into a more workable form. This technique replaces an integral variable with a new one, reducing the complexity. In our scenario, the integral \( \int \frac{d x}{\sqrt{1-16 x^{2}}} \) was transformed by setting \( x = \frac{1}{4} \sin(\theta) \).
- Upon substituting, \( dx \) translates to \( \frac{1}{4} \cos(\theta) d\theta \), and the denominator simplifies to \( \cos(\theta) \).
- This simplification leads to a much easier integral \( \int \frac{1}{4} d\theta \).