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 283: 15

Answer

zeros: $-5, 1,$ and $2$ $P(x)=(x-1)(x-2)(x+5)$

Work Step by Step

$P(x)=x^{3}+2x^{2}-13x+10$ $a_{0}=10 \qquad $p: $\pm 1,\pm 2,\pm 5,\pm 10$ $a_{n}=1,\qquad $q: $\pm 1, $ Possible rational zeros $\displaystyle \frac{p}{q}:\quad \pm 1,\pm 2,\pm 5,\pm 10$ Test $x=1 $ by synthetic division: $\left[\begin{array}{lllllll} \underline{1|} & 1 & 2 & -13 & 10 & & \\ & & 1 & 3 & -10 & & \\ & -- & -- & -- & -- & & \\ & 1 & 3 & -10 & \underline{|0} & \Rightarrow & P(1)=0, \end{array}\right.$ $1$ is a zero, $(x-1) $ is a factor of $P(x).$ The bottom row gives coefficients of the quotient. $P(x)=x^{3}+2x^{2}-13x+10=(x-1)(x^{2}+3x-10)$ We can factor the second parentheses: find factors of -10 that add to +3 ... (5 and -2) $P(x)=(x-1)(x-2)(x+5)$ So, the zeros are $-5, 1,$ and $2$
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