Algebra 2 (1st Edition)

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

Chapter 5 Polynomials and Polynomial Functions - 5.7 Apply the Fundamental Theorem of Algebra - Guided Practice for Example 4 - Page 382: 10

Answer

$4$ positive real zeros $2$ positive real zeros and $2$ imaginary zeros $4$ imaginary zeros

Work Step by Step

We are given the function: $$g(x)=2x^4-8x^3+6x^2-3x+1.$$ First we count the number of sign changes: $$+,-,+,-,+.$$ The coefficients of $g(x)$ have $4$ sign changes, so $g$ has either $4$ positive real zeros, or $2$ positive real zeros or $0$ positive real zeros. We determine $g(-x)$: $$\begin{align*} g(-x)&=2(-x)^4-8(-x)^3+6(-x)^2-3(-x)+1\\ &=2x^4+8x^3+6x^2+3x+1. \end{align*}$$ We count the number of sign changes: $$+,+,+,+,+.$$ The coefficients of $g(-x)$ have no change of sign, therefore there is no negative real zero. To summarize the results, we use a table: \[ \begin{array}{|c|c|c|c|} \hline \text{Positive}& \text{Negative} & \text{Imaginary} & \text{Total} \\ \text{real zeros} & \text{real zeros} & \text{zeros} & \text{zeros}\\ \hline 4 &0 & 0&4\\ \hline 2 & 0 &2&4\\ \hline 0 & 0 & 4&4\\ \hline \end{array}\]
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