College Algebra (10th Edition)

Published by Pearson
ISBN 10: 0321979478
ISBN 13: 978-0-32197-947-6

Chapter R - Section R.7 - Rational Expressions - R.7 Assess Your Understanding - Page 72: 82

Answer

The answer is $\dfrac{(x+3)(x^2-x-15)}{x(4x^2+5x+3)}$.

Work Step by Step

The simplification of the numerator can be done as follows: $\dfrac{2x+5}{x}-\dfrac{x}{x-3}$ $=\dfrac{(2x+5)(x-3)-x^2}{x(x-3)}$ [ Take LCM of the rationals ] $=\dfrac{2x^2-6x+5x-15-x^2}{x(x-3)}$ [ Expand the product ] $=\dfrac{x^2-x-15}{x(x-3)}$ [ Simplify by adding/subtracting like terms as needed] The simplification of the denominator can be done as follows: $\dfrac{x^2}{x-3}-\dfrac{(x+1)^2}{x+3}$ $=\dfrac{x^2(x+3)-(x-3)(x+1)^2}{(x-3)(x+3)}$ [ Take LCM of rationals] $=\dfrac{x^3+3x^2-(x-3)(x^2+2x+1)}{(x-3)(x+3)}$ [Expand and simplify] $=\dfrac{x^3+3x^2-x^2(x-3)-2x(x-3)-(x-3)}{(x-3)(x+3)}$ $=\dfrac{x^3+3x^2-x^3+3x^2-2x^2+6x-x+3}{(x-3)(x+3)}$ [ Add/ subtract like terms] $=\dfrac{4x^2+5x+3}{(x-3)(x+3)}$ Thus, the given expression can be simplified as follows: $\dfrac{\dfrac{2x+5}{x}-\dfrac{x}{x-3}}{\dfrac{x^2}{x-3}-\dfrac{(x+1)^2}{x+3}}$ $=\dfrac{\dfrac{x^2-x-15}{x(x-3)}}{\dfrac{4x^2+5x+3}{(x-3)(x+3)}}$ $=\dfrac{(x^2-x-15)(x-3)(x+3)}{x(4x^2+5x+3)(x-3)}$ [Reciprocate and multiply] $=\dfrac{(x^2-x-15)(x+3)}{x(4x^2+5x+3)}$ [Cancel common factor] Therefore, the simplified expression is $\dfrac{(x^2-x-15)(x+3)}{x(4x^2+5x+3)}$.
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