Algebra 1

Published by Prentice Hall
ISBN 10: 0133500403
ISBN 13: 978-0-13350-040-0

Chapter 9 - Quadratic Functions and Equations - 9-5 Completing the Square - Practice and Problem-Solving Exercises - Page 564: 14



Work Step by Step

$r^2-4r=30$ Compare it with the standard form of quadratic equation $ax^2+bx+c$, we have $a=1, b=-4$ Therefore, $b^2=4ac$ $\implies$ $c=\dfrac{b^2}{4a}$ Thus, $c=\dfrac{b^2}{4a}=\dfrac{(-4)^2}{4}=4$ To complete the square, add $4$ on both sides. $r^2-4r+4=30+4$ $\implies (r-2)^2=34$ $\implies r-2=5.8$ and $\implies r-2=-5.8$ or, $r=7.8,-3.8$
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