Chapter 8: Problem 35
Use integration tables to find the indefinite integral. \(\int \frac{x}{\sqrt{x^{4}-6 x^{2}+5}} d x\)
Short Answer
Expert verified
\( \frac{1}{2} Arcsec(x^{2}-3) + C \)
Step by step solution
01
Recognize Pattern
Recognize the integral as a derivative of the arcsecant function. The derivative of \( Arcsec(u) \) is \( \frac{1}{|u|\sqrt{u^{2}-1}} \). The given integral matches this pattern: \( \int \frac{u'}{|u|\sqrt{u^{2}-1}} du \), where \( u = x^{2} \), and \( x = \sqrt{u} \). Therefore, we will use these substitutions in the next steps.
02
Substitute variables
Rewrite the integral with the new variable \( u \) and its derivative \( du \). Here, by Chain Rule, the derivative \( du \) is \( 2xdx \). The integral thus becomes: \( \frac{1}{2} \int \frac{du}{\sqrt{u^{2}-6u+5}} \). Notice that the factor of 1/2 is factored out by the constant coefficient rule for integrals.
03
Complete the Square to match the pattern
Rewrite the expression \( u^{2}-6u+5 \) in the denominator as a perfect square. This is done by completing the square: \( u^{2}-6u+5 = (u-3)^{2}-4 \). Replace this expression in the integral. It now looks like this: \( \frac{1}{2} \int \frac{du}{\sqrt{(u-3)^{2}-4}} \). This pattern matches the derivative of \( Arcsec(u) \) where \( u \) is replaced by \( u-3 \).
04
Integration using Integral Tables
Recall that the integral of \( \frac{du}{|u|\sqrt{u^{2}-1}} \) is \( Arcsec(u) + C \). Here, \( u-3 \) is replaced by \( u \). Therefore, the integral is: \( \frac{1}{2} Arcsec(u-3) + C \).
05
Re-substitute \( u \) with \( x^{2} \)
Re-substitute \( u \) with \( x^{2} \) into the integral: \( \frac{1}{2} Arcsec(x^{2}-3) + C \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Arcsecant Function
The arcsecant function, denoted as \( \text{Arcsec}(u) \), is the inverse of the secant function. This means it helps us find an angle whose secant is \( u \). In calculus, the derivative of the arcsecant function reveals unique patterns that are essential for integration. Specifically, if \( u \) is a differentiable function of \( x \), then the derivative of \( \text{Arcsec}(u) \) is given by \( \frac{1}{|u| \sqrt{u^2 - 1}} \).
- The presence of \( |u| \) denotes absolute value, ensuring the function behaves correctly across its domain.
- The \( \sqrt{u^2 - 1} \) indicates that the expression under square root must remain positive for real number operations.
Indefinite Integral
An indefinite integral represents a family of functions whose derivatives equal the integrand. It's written as \( \int f(x) \, dx = F(x) + C \), where \( C \) is the constant of integration. Indefinite integrals are essential because they provide a way to reverse differentiation.
- The symbol \( \int \) signifies integration, aimed to 'accumulate' or 'summarize' the function \( f(x) \).
- \( C \) emphasizes the general solution nature, capturing all possible outcomes from antiderivatives.
Substitution Method
The substitution method is a powerful technique in integration that simplifies integrals by transforming variables. It involves identifying a portion of the integral to substitute with a new variable. This technique changes the function into a form that's easier to integrate.
In the exercise:
In the exercise:
- The substitution \( u = x^2 \) is introduced. This choice stems from identifying \( x^2 \) as a central component of the integral's pattern.
- The derivative \( du = 2x \, dx \) redefines the expression's variables, simplifying the integral as \( \frac{1}{2} \int \frac{du}{\sqrt{u^2 - 6u + 5}} \).
Completing the Square
Completing the square is an algebraic method employed to rewrite quadratic expressions of the form \( ax^2 + bx + c \) into \( (x - h)^2 - k \) or similar forms. This transformation eases the process of integration and finding real roots or extrema.
- In the provided solution, \( u^2 - 6u + 5 \) becomes \( (u - 3)^2 - 4 \).
- This makes the expression inside the integral align with the known derivative form of the arcsecant function, \( \text{Arcsec}(u) \).