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Ch. 8 - Integration Techniques
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 8, Problem 8.5.3c

3. What term(s) should appear in the partial fraction decomposition of a proper rational function with each of the following?
c. A factor of (x² + 2x + 6) in the denominator

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1
Identify that the factor given, \(x^2 + 2x + 6\), is an irreducible quadratic factor because its discriminant \(\Delta = b^2 - 4ac = 2^2 - 4 \cdot 1 \cdot 6 = 4 - 24 = -20 < 0\), which means it cannot be factored further over the real numbers.
Recall that for an irreducible quadratic factor \(ax^2 + bx + c\) in the denominator, the corresponding term in the partial fraction decomposition has the form \(\frac{Ax + B}{ax^2 + bx + c}\), where \(A\) and \(B\) are constants to be determined.
If the factor \(x^2 + 2x + 6\) appears with multiplicity 1 (i.e., it is not repeated), then the partial fraction term is simply \(\frac{Ax + B}{x^2 + 2x + 6}\).
If the factor appears with multiplicity greater than 1, say \(n\), then the decomposition includes terms for each power from 1 up to \(n\): \(\frac{A_1x + B_1}{x^2 + 2x + 6} + \frac{A_2x + B_2}{(x^2 + 2x + 6)^2} + \cdots + \frac{A_nx + B_n}{(x^2 + 2x + 6)^n}\).
Summarize that the key point is that each irreducible quadratic factor in the denominator corresponds to a numerator that is a linear polynomial \(Ax + B\) over that quadratic factor in the partial fraction decomposition.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Partial Fraction Decomposition

Partial fraction decomposition is a method used to express a proper rational function as a sum of simpler fractions whose denominators are factors of the original denominator. This technique simplifies integration and other operations by breaking complex fractions into manageable parts.
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Irreducible Quadratic Factors

An irreducible quadratic factor is a quadratic polynomial that cannot be factored further over the real numbers. In partial fraction decomposition, such factors in the denominator correspond to terms with linear numerators, for example, (Ax + B)/(quadratic factor).
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Proper Rational Function

A proper rational function is a fraction where the degree of the numerator is less than the degree of the denominator. This condition ensures that partial fraction decomposition can be applied directly without polynomial division.
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