Algebra 2 Common Core

Published by Prentice Hall
ISBN 10: 0133186024
ISBN 13: 978-0-13318-602-4

Chapter 5 - Polynomials and Polynomial Functions - 5-6 The Fundamental Theorem of Algebra - Practice and Problem-Solving Exercises - Page 324: 56

Answer

$x = \dfrac{-5 \pm i\sqrt {47}}{4}$

Work Step by Step

Write the given equation in standard form to obtain $$2x^2+5x+9=0$$ We are asked to use the quadratic equation to factor this polynomial. The quadratic equation is given by the formula: $x = \dfrac{-b \pm \sqrt {b^2 - 4ac}}{2a}$ where $a$ is the coefficient of the $x^2$ term, $b$ is the coefficient of the $x$ term, and $c$ is the constant. The given equation has $a=2, b=5, $ and $c=9$. Plug these values into the formula to obtain: $x = \dfrac{-5 \pm \sqrt {5^2 - 4(2)(9)}}{2(2)}$ $x = \dfrac{-5 \pm \sqrt {25 - 72}}{4}$ $x = \dfrac{-5 \pm \sqrt {-47}}{4}$ The number $-47$ can be factored as $47(-1)$ so: $x = \dfrac{-5 \pm \sqrt {(47)(-1)}}{4}$ We can bring out the square root of $-1$ which is $i$, to obtain: $x = \dfrac{-5 \pm i\sqrt {47}}{4}$ We cannot simplify this equation any further, so the solution is: $x = \frac{-5 ± i\sqrt {47}}{4}$
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