Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 3 - Section 3.4 - Real Zeros of Polynomials - 3.4 Exercises - Page 284: 42

Answer

$P(x)=(x+1)(x-2)^2(x+2)(x-3)$ zeros: $\quad -2, -1, 2, 3$

Work Step by Step

$P(x)=x^{5}-4x^{4}-3x^{3}+22x^{2}-4x-24,$ ($3$ sign variations, we expect $3$ or $1$ real zeros) $P(-x)=-x^{5}-4x^{4}+3x^{3}+22x^{2}+4x-24,$ ($2$ sign variations, we expect $2 $or $0$ negative real zero) $a_{0}=-24 \quad $p: $\pm 1,\pm 2,\pm 3,\pm 4,\pm 6,\pm 12,\pm 24$ $a_{n}=1,\qquad $q: $\pm 1,\pm 2,\pm 4$ Possible rational zeros $\displaystyle \frac{p}{q}:\quad$ with synthetic division, we try$ \pm$1, $\pm$2,... $\begin{array}{r|rrrrrrrrrrr}\hline -1 & 1 & -4 & -3 & 22 & -4 & -24 & \\ & & -1 & 5 & -2 & -20 & 24 & \\ \hline & 1 & -5 & 2 & 20 & -24 & 0 & \\ & & & \swarrow & & & & \\ 2 & 1 & -5 & 2 & 20 & -24 & & \\ & & 2 & -6 & -8 & 24 & & \\ \hline & 1 & -3 & -4 & 12 & 0 & & \\ & & \swarrow & & & & \\ 2 & 1 & -3 & -4 & 12 & & & \\ & & 2 & -2 & -12 & & & \\ \hline & 1 & -1 & -6 & 0 & & & \\ & & \swarrow & & & & \\ -2 & 1 & -1 & -6 & & & & \\ & & -2 & 6 & & & & \\ \hline & 1 & -3 & 0 & & & & \\ & & & & & & & \\ 3 & 1 & -3 & & & & & \\ & & 3 & & & & & \\ \hline & 1 & 0 & & & & & \end{array}$ $P(x)=(x+1)(x-2)(x-2)(x+2)(x-3)$ zeros: $\quad -2, -1, 2, 3$
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