College Algebra (11th Edition)

Published by Pearson
ISBN 10: 0321671791
ISBN 13: 978-0-32167-179-0

Chapter 1 - Section 1.4 - Quadratic Equations - 1.4 Exercises - Page 113: 91

Answer

2 rational solutions

Work Step by Step

$\bf{\text{Solution Outline:}}$ To evaluate the discriminant of the given equation, $ 8x^2-72=0 ,$ identify first the value of $a,b,$ and $c$ in the quadratic expression $ax^2+bx+c.$ Then use the Discriminant Formula. If the value of the discriminant is less than zero, then there are $\text{ 2 nonreal complex solutions .}$ If the value is $0,$ then there is $\text{ 1 distinct rational solution .}$ If the value of the discriminant is a positive perfect square, then there are $\text{ 2 rational solutions .}$ Finally, if the value of the discriminant is positive but not a perfect square, there are $\text{ 2 irrational solutions .}$ $\bf{\text{Solution Details:}}$ In the equation above, $a= 8 ,$ $b= 0 ,$ and $c= -72 .$ Using the Discriminant Formula which is given by $b^2-4ac,$ the value of the discriminant is \begin{array}{l}\require{cancel} (0)^2-4(8)(-72) \\\\= 2304 \\\\= 48^2 .\end{array} Since the discriminant is $\text{ a positive perfect square ,}$ then there are $\text{ 2 rational solutions .}$
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