Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Appendix A - Review - A.7 Complex Numbers; Quadratic Equations in the Complex Number System - A.7 Assess Your Understanding - Page A61: 64

Answer

$\left\{-\dfrac{3}{10}-\dfrac{1}{10}i,\dfrac{3}{10}+\dfrac{1}{10}i \right\}$.

Work Step by Step

The given equation has $a=10,b=6$ and $c=1$. The discriminant is $=b^2-4ac$ $=(6)^2-4(10)(1)$ $=36-40$ $=-4$ Use Quadratic formula. $x=\dfrac{-b\pm \sqrt {b^2-4ac}}{2a}$ Substitute the values of $a, b, c, $ and discriminant to obtain: $x=\dfrac{-(6)\pm \sqrt {-4}}{2(10)}$ Simplify. $x=\dfrac{-6\pm \sqrt{4(-1)}}{20}$ $x=\dfrac{-6\pm 2i}{20}$ Factor out $2$. $x=\dfrac{2(-3\pm i)}{20}$ Cancel the common factor $2$. $x=\dfrac{-3\pm i}{10}$ The equation has two solutions: $-\frac{3}{10}-\frac{i}{10}$ and $-\frac{3}{10}+\frac{i}{10}$. Check: For $x=-\frac{3}{10}-\frac{i}{10}$. $=10(-\frac{3}{10}-\frac{i}{10})^2+6(-\frac{3}{10}-\frac{i}{10})+1$ $=10(\frac{9}{100}+2\cdot \frac{3i}{100}+\frac{i^2}{100})-\frac{9}{5}-\frac{3i}{5}+1$ $=\frac{9}{10}+\frac{3i}{5}+\frac{i^2}{10}-\frac{9}{5}-\frac{3i}{5}+1$ $=\frac{1}{10}+\frac{i^2}{10}$ $=\frac{1}{10}-\frac{1}{10}$ $=0$ For $x=-\frac{3}{10}+\frac{i}{10}$. $=10(-\frac{3}{10}+\frac{i}{10})^2+6(-\frac{3}{10}+\frac{i}{10})+1$ $=10(\frac{9}{100}-2\cdot \frac{3i}{100}+\frac{i^2}{100})-\frac{9}{5}+\frac{3i}{5}+1$ $=\frac{9}{10}-\frac{3i}{5}+\frac{i^2}{10}-\frac{9}{5}+\frac{3i}{5}+1$ $=\frac{1}{10}+\frac{i^2}{10}$ $=\frac{1}{10}-\frac{1}{10}$ $=0$ Hence, the solution set is $\left\{-\dfrac{3}{10}-\dfrac{1}{10}i,\dfrac{3}{10}+\dfrac{1}{10}i \right\}$.
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