Intermediate Algebra (6th Edition)

Published by Pearson
ISBN 10: 0321785045
ISBN 13: 978-0-32178-504-6

Chapter 8 - Section 8.1 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 485: 50

Answer

The solutions are $x=2$ and $x=-\dfrac{2}{3}$

Work Step by Step

$3x^{2}-4x=4$ Take out common factor $3$ from the left side of the equation: $3\Big(x^{2}-\dfrac{4}{3}x\Big)=4$ Take $3$ to divide the right side: $x^{2}-\dfrac{4}{3}x=\dfrac{4}{3}$ Add $\Big(\dfrac{b}{2}\Big)^{2}$ to both sides of the equation. In this particular case, $b=-\dfrac{4}{3}$: $x^{2}-\dfrac{4}{3}x+\Big(-\dfrac{4}{3\cdot2}\Big)^{2}=\dfrac{4}{3}+\Big(-\dfrac{4}{3\cdot2}\Big)^{2}$ $x^{2}-\dfrac{4}{3}x+\dfrac{4}{9}=\dfrac{4}{3}+\dfrac{4}{9}$ $x^{2}-\dfrac{4}{3}x+\dfrac{4}{9}=\dfrac{16}{9}$ Factor the left side of the equation, which is a perfect square trinomial: $\Big(x-\dfrac{2}{3}\Big)^{2}=\dfrac{16}{9}$ Take the square root of both sides: $\sqrt{\Big(x-\dfrac{2}{3}\Big)^{2}}=\pm\sqrt{\dfrac{16}{9}}$ $x-\dfrac{2}{3}=\pm\dfrac{4}{3}$ Solve for $x$: $x=\pm\dfrac{4}{3}+\dfrac{2}{3}$ $x=\dfrac{4}{3}+\dfrac{2}{3}=\dfrac{6}{3}=2$ $x=-\dfrac{4}{3}+\dfrac{2}{3}=-\dfrac{2}{3}$ The solutions are $x=2$ and $x=-\dfrac{2}{3}$
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