Intermediate Algebra: Connecting Concepts through Application

Published by Brooks Cole
ISBN 10: 0-53449-636-9
ISBN 13: 978-0-53449-636-4

Chapter 7 - Rational Functions - 7.4 Adding and Subtracting Rational Expressions - 7.4 Exercises - Page 590: 51

Answer

$\frac{2(3h - 26)}{(h - 7)(h - 2)(h - 8)}$

Work Step by Step

To add or subtract rational expressions, we need to make sure that the expressions have the same denominator. We need to rewrite the two expressions with the same denominator, so we need to find the least common denominator (LCD) for both expressions. The first thing we want to do is to make sure that each denominator is factored completely. We see that the denominators are quadratic expressions, which are given by the formula: $ax^2 + bx + c$, where $a$, $b$, and $c$ are all real numbers. To factor the expression in the denominator of the first fraction, we want to find which factors when multiplied will give us the product of the $a$ and $c$ terms, which is $14$, but when added together will give us the $b$ term, which is $-9$. This means that both factors should be negative. Let's look at possible factors: $-7$ and $-2$ $-14$ and $-1$ It looks like the first combination will work. Let's rewrite the expression in factor form: $(h - 7)(h - 2)$ To factor the expression in the denominator of the second fraction, we want to find which factors when multiplied will give us the product of the $a$ and $c$ terms, which is $16$, but when added together will give us the $b$ term, which is $-10$. This means that both factors are negative. Let's look at possible factors: $-8$ and $-2$ $-16$ and $-1$ It looks like the first combination will work. Let's rewrite the expression in factor form: $(h - 8)(h - 2)$ The exercise can now be rewritten as: $\frac{h + 3}{(h - 7)(h - 2)} - \frac{h - 4}{(h - 8)(h - 2)}$ Next, we want to find the least common denominator (LCD). We do this by taking the highest power of each factor in the denominators of the fractions. Before we can do that, we need to factor the denominators: LCD = $(h - 7)(h - 2)(h - 8)$ Now that we have the least common denominator, we multiply the numerator of each fraction with the factor or factors it is missing in its denominator: $\frac{(h + 3)(h - 8)}{(h - 7)(h - 2)(h - 8)} - \frac{(h - 4)(h - 7)}{(h - 7)(h - 2)(h - 8)}$ Rewrite the two fractions as one with the same denominator: $\frac{(h + 3)(h - 8) - (h - 4)(h - 7)}{(h - 7)(h - 2)(h - 8)}$ Use the distributive property to rewrite the numerator: $\frac{(h^2 - 5h - 24) - (h^2 - 11h + 28)}{(h - 7)(h - 2)(h - 8)}$ Combine like terms in the numerator: $\frac{6h - 52}{(h - 7)(h - 2)(h - 8)}$ Factor what is common to the terms in the numerator: $\frac{2(3h - 26)}{(h - 7)(h - 2)(h - 8)}$
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