Chapter 9: Problem 605
For the following exercises, write the partial fraction decomposition. $$ \frac{-8 x-30}{x^{2}+10 x+25} $$
Short Answer
Expert verified
\( \frac{-8}{x+5} + \frac{10}{(x+5)^2} \).
Step by step solution
01
Recognize the Denominator
First, observe the denominator \( x^2 + 10x + 25 \), which appears to be a perfect square trinomial.
02
Factor the Denominator
Factor the quadratic expression \( x^2 + 10x + 25 \) as \((x + 5)^2\). This indicates that the original fraction can be decomposed using these factors.
03
Set Up the Partial Fraction Decomposition
The partial fraction decomposition for \( \frac{-8x - 30}{(x + 5)^2} \) is given by \( \frac{A}{x + 5} + \frac{B}{(x + 5)^2} \).
04
Clear the Denominator
Multiply both sides by \((x + 5)^2\) to eliminate the fractions: \(-8x - 30 = A(x + 5) + B\).
05
Expand and Collect Terms
Expand the right side: \(-8x - 30 = A(x + 5) + B = Ax + 5A + B\).
06
Equate the Coefficients
Match the coefficients from both sides: For \(x\), \(-8 = A\). For the constant term, \(-30 = 5A + B\).
07
Solve the System of Equations
Substitute \(A = -8\) into the second equation: \(-30 = 5(-8) + B\) \(-30 = -40 + B\) \(B = 10\).
08
Write the Partial Fraction Decomposition
Substitute \(A\) and \(B\) back into the partial fractions: \(\frac{-8}{x + 5} + \frac{10}{(x + 5)^2}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Factoring Quadratics
Factoring quadratic equations is a critical step in many algebraic processes, including partial fraction decomposition. A quadratic equation usually takes the form \( ax^2 + bx + c \). In some cases, like \( x^2 + 10x + 25 \), it appears as a perfect square trinomial. This means it can be expressed in the form \( (x + d)^2 \). For our specific example:
- The trinomial \( x^2 + 10x + 25 \) is factored as \( (x + 5)^2 \).
Partial Fractions
The process of partial fractions is about expressing a complex fraction as a sum of simpler fractions. This is particularly useful for integration and solving differential equations. By writing \( \frac{-8x - 30}{(x + 5)^2} \) as the sum \( \frac{A}{x + 5} + \frac{B}{(x + 5)^2} \), we break it into easier parts.Here's why it works:
- Each part of the decomposition corresponds to a factor in the denominator, and each term needs to capture all the "views" of the factors.
- In this case, \( \frac{-8x - 30}{(x + 5)^2} \) has a repeated linear factor, so we use two terms: one with \( x + 5 \) and one with \( (x + 5)^2 \).
Solving Equations
Solving the resulting equations in partial fraction decomposition involves algebraic manipulation until each coefficient can be clearly defined. After setting up the partial fractions:
- The equation \( -8x - 30 = A(x+5) + B \) is formed by removing the denominator.
- For \( x \), compare coefficients to find \( A \).
- For constant terms, solve a straightforward equation to determine \( B \).