College Algebra (10th Edition)

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

Chapter 1 - Section 1.4 - Radical Equations; Equations Quadratic in Form; Factorable Equations - 1.4 Assess Your Understanding - Page 118: 61

Answer

$x_{1}=\frac{1889+441\sqrt{17}}{512}$ $x_{2}=\frac{1889-441\sqrt{17}}{512}$

Work Step by Step

The quadratic formula will be used, but before doing so, $x^{1/4}=u$ therefore: $4u^2-9u+4=0$ $u=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$ where a=4, b=-9, and c=4 $u=\frac{-(-9)\pm\sqrt{(-9)^2-4(4)(4)}}{2(4)}$ $u=\frac{9\pm\sqrt{81-64}}{8}$ $u=\frac{9\pm\sqrt{17}}{8}$ There are two solutions: First: $x^{1/4}=\frac{9+\sqrt{17}}{8}$ $(x^{1/4})^4=(\frac{9+\sqrt{17}}{8})^4$ $x=(\frac{9^4+4(9^3)(\sqrt{17})+6(9^2)(\sqrt{17})^2+4(9)(\sqrt{17})^3+(\sqrt{17})^4}{8^4})$ $x=\frac{6561+2916(\sqrt{17})+8262+612(\sqrt{17})+289}{4096}$ $x=\frac{15112+3528\sqrt{17}}{4096}$ $x=\frac{1889+441\sqrt{17}}{512}$ Second: $x^{1/4}=\frac{9-\sqrt{17}}{8}$ $(x^{1/4})^4=(\frac{9-\sqrt{17}}{8})^4$ $x=(\frac{9^4-4(9^3)(\sqrt{17})+6(9^2)(\sqrt{17})^2-4(9)(\sqrt{17})^3+(\sqrt{17})^4}{8^4})$ $x=\frac{6561-2916(\sqrt{17})+8262-612(\sqrt{17})+289}{4096}$ $x=\frac{15112-3528\sqrt{17}}{4096}$ $x=\frac{1889-441\sqrt{17}}{512}$
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