Chapter 8: Problem 18
In Exercises \(17-20\), express the integrand as a sum of partial fractions and evaluate the integrals. $$\int_{-1}^{0} \frac{x^{3} d x}{x^{2}-2 x+1}$$
Short Answer
Expert verified
The integral evaluates to \(-2\).
Step by step solution
01
Identify the Denominator as a Perfect Square
First, notice that the denominator \(x^2 - 2x + 1\) is a perfect square. It can be rewritten as \((x-1)^2\).
02
Express the Integrand in Partial Fractions
The integrand \(\frac{x^3}{(x-1)^2}\) already has \((x-1)^2\) as the denominator, and \(x^3\) is the numerator. Since the denominator is a power of a linear factor, a partial fraction decomposition can be written as \(\frac{x^3}{(x-1)^2} = \frac{A}{x-1} + \frac{B}{(x-1)^2}\).
03
Determine the Values of A and B
To find \(A\) and \(B\), multiply through by \((x-1)^2\) to clear the denominators: \(x^3 = A(x-1) + B\). Expand and combine like terms: \(x^3 = Ax - A + B\). Equate coefficients to find \(A = 1\) and \(B = 1\) (assuming you equate with \(x^3 - x = 0\)).
04
Rewrite the Integrand with Determined Coefficients
Substitute \(A\) and \(B\) back into the partial fraction expression: \(\frac{x^3}{(x-1)^2} = \frac{x}{x-1} + \frac{1}{(x-1)^2}\).
05
Integrate Each Term Separately
Now integrate each term separately: \(\int_{-1}^{0} \frac{x}{x-1} \, dx \) and \(\int_{-1}^{0} \frac{1}{(x-1)^2} \, dx \). Start with the first term; use the substitution \(u = x-1, \; du = dx\) for both integrals.
06
Integrate the First Term
The integral \(\int \frac{x}{x-1} \, dx\) transforms into \(\int \frac{x}{u} \, du\), which can further be evaluated by substitution \(u = x - 1\), resulting in \(\int \left(\frac{x}{x-1} + 1\right) \, dx - \int 1 dx\). Simplifies to \(\int \left(1 + \frac{1}{(x-1)}\right)\,dx\).
07
Integrate the Second Term
The integral \(\int \frac{1}{(x-1)^2} \, dx\) uses the power rule for integration, resulting in \(-\frac{1}{x-1}\).
08
Evaluate the Definite Integrals
Evaluate each integral between the bounds \(-1\) and \(0\). Substitute the bounds into the integrated expressions and simplify. Sum the definite integrals of both terms.
09
Simplify the Evaluation
Perform the calculations: the definite integral of each term with the bounds \(-1\) to \(0\). Sum \([-2 - (0) - (-2) + 0]\) to yield a final value of \(-2\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Partial Fraction Decomposition
Partial fraction decomposition is a technique used in calculus to simplify complex rational expressions, making them easier to integrate. It involves breaking down a single rational fraction into a sum of simpler fractions. This method is particularly useful when dealing with integrals of rational functions.
- Identify the type of decomposition needed: Look at the factors in the denominator to determine how to split up the fraction.
- Set up the partial fraction decomposition: Express the original fraction as a sum of simpler fractions, each with an undetermined constant.
- Determine coefficients: Multiply through by the common denominator to clear the fractions, then use algebraic techniques to find the constants.
Definite Integral
A definite integral is a fundamental concept in calculus, representing the area under a curve over a specific interval. Unlike indefinite integrals, definite integrals result in a numerical value that quantifies this area.
- Evaluate definite integrals by computing the antiderivative of the function within the given bounds.
- The notation \( \int_{a}^{b} f(x) \, dx \) denotes integration from \(a\) to \(b\).
Power Rule Integration
Power rule integration is one of the most straightforward techniques for finding antiderivatives. It applies to terms of the form \( x^n \), where \(n\) is a real number.
- For a function \( x^n \), the antiderivative is \( \frac{x^{n+1}}{n+1} + C \), where \(n eq -1\) and \(C\) is the constant of integration for indefinite integrals.
- The power rule allows for the quick evaluation of integrals of polynomial terms.