Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 4 Quadratic Functions and Factoring - 4.7 Complete the Square - 4.7 Exercises - Skill Practice - Page 289: 56


The solutions are $6+3i\sqrt{6}$ and $6-3i\sqrt{6}$.

Work Step by Step

$ 0.1x^{2}-x+9=0.2x\qquad$ ...add $-0.2x$ to each side $ 0.1x^{2}-1.2x+9=0\qquad$ ...write the expression in the form $ax^{2}+bx=c$ $ 0.1x^{2}-1.2x=-9\qquad$ ...multiply the entire expression with $10$. $ x^{2}-12x=90\qquad$ ...square half the coefficient of $x$. $(\displaystyle \frac{-12}{2})^{2}=(6)^{2}=36\qquad$ ...complete the square by adding $36$ to each side of the expression $ x^{2}-12x+36=-90+36\qquad$ ...Write $x^{2}-12x+36$ as a binomial squared. $(x-6)^{2}=-54\qquad$ ...take square roots of each side. $ x-6=\pm\sqrt{-54}\qquad$ ...simplify $\sqrt{-54}=i\sqrt{54}=i\sqrt{9\cdot 6}=3i\sqrt{6}$ $ x-6=\pm 3i\sqrt{6}\qquad$ ...add $6$ to each side. $x=6\pm 3i\sqrt{6}$
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