College Algebra (6th Edition)

Published by Pearson
ISBN 10: 0-32178-228-3
ISBN 13: 978-0-32178-228-1

Chapter 8 - Summary, Review, and Test - Cumulative Review Exercises (Chapters 1-8) - Page 792: 16

Answer

$x: (-\frac{2}{3}, \frac{3}{2})$

Work Step by Step

$$6x^{2} - 6 \lt 5x$$ Re-writing the inequality results in $6x^{2} - 5x - 6 \lt0$ which is in a quadratic form. To find the values of x, we can use the quadratic formula $\frac{-b \frac{+}{} \sqrt {b^{2} - 4ac}}{2a}$: $$\frac{-(-5) \frac{+}{} \sqrt {(-5)^{2} - 4(6)(-6)}}{2(6)}$$ $$\frac{5 \frac{+}{} \sqrt {25 + 144}}{12}$$ $$\frac{5 \frac{+}{} \sqrt {169}}{12}$$ $$\frac{5 \frac{+}{} 13}{12}$$ where $x$ is $\frac{5 + 13}{12} = \frac{18}{12} = \frac{3}{2}$, and also $\frac{5 - 13}{12} = \frac{-8}{12} = -\frac{2}{3}$ This means that we can write the original inequality in the following manner: $$(x-\frac{3}{2})(x+\frac{2}{3})\lt0$$ and solve each term independently:$$x-\frac{3}{2}\lt0$$$x\lt0+\frac{3}{2}$ $x\lt\frac{3}{2}$$$x + \frac{2}{3}\lt0$$$x\lt0-\frac{2}{3}$ $x\lt-\frac{2}{3}$ To find the domain of the inequality, we now use 3 values of $x$ (a value less than $-\frac{2}{3}$, a value between $-\frac{2}{3}$ and $\frac{3}{2}$, and a value greater than $\frac{3}{2}$) to test if they satisfy the conditions of the original inequality:$$6x^{2} - 6 \lt 5x$$$6(-1)^{2} - 6\lt5(-1)$ $0\lt-5$ which is not true. $6(0)^{2} - 6\lt5(0)$ $-6\lt0$ which is true $6(2)^{2} - 6\lt5(2)$ $6(4) - 6 \lt 10$ $18\lt10$ which is not true. We therefore conclude that the domain for this inequality is {$x|-\frac{2}{3}\lt x \lt\frac{3}{2}$, where $x$ belongs to the realm of Real numbers}, also expressed as $x: (-\frac{2}{3}, \frac{3}{2})$ since neither term is included within the domain.
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