Why is answer A+B=1 and 2A-3B=-2 ?

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Question
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Why is answer A+B=1 and 2A-3B=-2 ?
The image shows a handwritten mathematical solution for the partial fraction decomposition of a rational function.

---

**Problem:**  
Given the rational function: 

\[ Y(s) = \frac{s - 2}{s^2 - s - 6} \]

Factor the denominator: 

\[ s^2 - s - 6 = (s - 3)(s + 2) \]

The function can be decomposed into partial fractions as follows: 

\[ \frac{s - 2}{(s - 3)(s + 2)} = \frac{A}{s - 3} + \frac{B}{s + 2} \]

**Steps to solve:**

1. **Clear the denominators:**

\[ s - 2 = A(s + 2) + B(s - 3) \]

2. **Expand and simplify:**

\[ A(s + 2) + B(s - 3) = As + 2A + Bs - 3B \]

Combine like terms: 

\[ (A + B)s + (2A - 3B) \]

3. **Compare coefficients:**

For the expression to equal \( s - 2 \), equate coefficients:

\[ A + B = 1 \]  
\[ 2A - 3B = -2 \]

This system of equations can be solved to find \( A \) and \( B \).

There are no graphs or additional diagrams included in the image.
Transcribed Image Text:The image shows a handwritten mathematical solution for the partial fraction decomposition of a rational function. --- **Problem:** Given the rational function: \[ Y(s) = \frac{s - 2}{s^2 - s - 6} \] Factor the denominator: \[ s^2 - s - 6 = (s - 3)(s + 2) \] The function can be decomposed into partial fractions as follows: \[ \frac{s - 2}{(s - 3)(s + 2)} = \frac{A}{s - 3} + \frac{B}{s + 2} \] **Steps to solve:** 1. **Clear the denominators:** \[ s - 2 = A(s + 2) + B(s - 3) \] 2. **Expand and simplify:** \[ A(s + 2) + B(s - 3) = As + 2A + Bs - 3B \] Combine like terms: \[ (A + B)s + (2A - 3B) \] 3. **Compare coefficients:** For the expression to equal \( s - 2 \), equate coefficients: \[ A + B = 1 \] \[ 2A - 3B = -2 \] This system of equations can be solved to find \( A \) and \( B \). There are no graphs or additional diagrams included in the image.
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