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Ch. 5 - Systems of Equations and Inequalities
Blitzer - College Algebra 8th Edition
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Capitolo 6, Problema 22

In Exercises 16–24, write the partial fraction decomposition of each rational expression. (7x^2 - 7x + 23)/(x - 3)(x^2 + 4)

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Step 1: Recognize that the given rational expression \((7x^2 - 7x + 23)/((x - 3)(x^2 + 4))\) needs to be decomposed into partial fractions. The denominator consists of two distinct factors: \(x - 3\) (a linear factor) and \(x^2 + 4\) (an irreducible quadratic factor).
Step 2: Set up the partial fraction decomposition. For the linear factor \(x - 3\), assign a constant \(A\) as the numerator. For the irreducible quadratic factor \(x^2 + 4\), assign a linear numerator \(Bx + C\). The decomposition will look like: \(\frac{7x^2 - 7x + 23}{(x - 3)(x^2 + 4)} = \frac{A}{x - 3} + \frac{Bx + C}{x^2 + 4}\).
Step 3: Multiply through by the denominator \((x - 3)(x^2 + 4)\) to eliminate the fractions. This gives: \(7x^2 - 7x + 23 = A(x^2 + 4) + (Bx + C)(x - 3)\).
Step 4: Expand the right-hand side of the equation. Distribute \(A\) across \(x^2 + 4\), and distribute \(Bx + C\) across \(x - 3\). This results in: \(7x^2 - 7x + 23 = A(x^2) + A(4) + Bx(x) + Bx(-3) + C(x) + C(-3)\). Combine like terms.
Step 5: Equate coefficients of \(x^2\), \(x\), and the constant terms on both sides of the equation. Solve the resulting system of equations to find the values of \(A\), \(B\), and \(C\). Substitute these values back into the partial fraction decomposition.

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Rational Expressions

A rational expression is a fraction where both the numerator and the denominator are polynomials. Understanding rational expressions is crucial for performing operations like addition, subtraction, and decomposition. In this context, the expression (7x^2 - 7x + 23)/(x - 3)(x^2 + 4) is a rational expression that needs to be decomposed into simpler fractions.
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Partial Fraction Decomposition

Partial fraction decomposition is a method used to express a rational function as a sum of simpler fractions. This technique is particularly useful for integrating rational expressions or simplifying complex algebraic fractions. The goal is to break down the given rational expression into components that are easier to work with, based on the factors of the denominator.
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Polynomial Factorization

Polynomial factorization involves breaking down a polynomial into its constituent factors, which can be linear or irreducible quadratic expressions. In the given rational expression, the denominator (x - 3)(x^2 + 4) consists of a linear factor and an irreducible quadratic factor. Recognizing these factors is essential for setting up the correct form for the partial fraction decomposition.
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