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: 66

Answer

$\left\{\dfrac{3}{13}-\dfrac{2}{13}i,\dfrac{3}{13}+\dfrac{2}{13}i\right\}$

Work Step by Step

Subtract $6x$ from both sides. $13x^2+1-6x=6x-6x$ Simplify by combining like terms. $13x^2-6x+1=0$ The quadratic equation above has $a=13,b=-6$ and $c=1$. The discriminant is $b^2-4ac$ $=(-6)^2-4(13)(1)$ $=36-52$ $=-16$ Use Quadratic formula. $x=\dfrac{-b\pm \sqrt {b^2-4ac}}{2a}$ Substitute the values of $a, b, c,$ and the discriminant:. $x=\dfrac{-(-6)\pm \sqrt {-16}}{2(13)}$ Simplify. $x=\dfrac{6\pm \sqrt{16(-1)}}{26}$ $x=\dfrac{6\pm 4i}{26}$ Factor out $2$. $x=\dfrac{2(3\pm 2i)}{26}$ Cancel the common factor $2$. $x=\dfrac{3\pm 2i}{13}$ The equation has two solutions: $\frac{3}{13}-\frac{2i}{13}$ and $\frac{3}{13}+\frac{2i}{13}$. Check: For $x=\frac{3}{13}-\frac{2i}{13}$. $=13(\frac{3}{13}-\frac{2i}{13})^2-6(\frac{3}{13}-\frac{2i}{13})+1$ $=13(\frac{9}{169}-2\cdot \frac{6i}{169}+\frac{4i^2}{169})-\frac{18}{13}+\frac{12i}{13}+1$ $=\frac{9}{13}-\frac{12i}{13}+\frac{4i^2}{13}-\frac{18}{13}+\frac{12i}{13}+1$ $=\frac{4}{13}+\frac{4i^2}{13}$ $=\frac{4}{13}-\frac{4}{13}$ $=0$ For $x=\frac{3}{13}+\frac{2i}{13}$. $=13(\frac{3}{13}+\frac{2i}{13})^2-6(\frac{3}{13}+\frac{2i}{13})+1$ $=13(\frac{9}{169}+2\cdot \frac{6i}{169}+\frac{4i^2}{169})-\frac{18}{13}-\frac{12i}{13}+1$ $=\frac{9}{13}+\frac{12i}{13}+\frac{4i^2}{13}-\frac{18}{13}-\frac{12i}{13}+1$ $=\frac{4}{13}+\frac{4i^2}{13}$ $=\frac{4}{13}-\frac{4}{13}$ $=0$ Hence, the solution set is $\left\{\dfrac{3}{13}-\dfrac{2}{13}i,\dfrac{3}{13}+\dfrac{2}{13}i\right\}$.
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