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: 37

Answer

Zeros:$\displaystyle \quad \frac{1}{2},\quad \frac{3}{4},\quad- \frac{2}{3}$ $P(x)=(2x-1)(4x-3)(3x+2)$

Work Step by Step

Possible rational zeros: $\displaystyle \quad \frac{p}{q}$ where$\left\{\begin{array}{llllllll} p: & \pm 1 & \pm 2 & \pm 3, & \pm 6 & & & \\ q: & \pm 1 & \pm 2, & \pm 3, & \pm 4, & \pm 6 & \pm 12 & \pm 24 \end{array}\right.$ $P(x)$ has 1 sign change, so we expect 1 positive real zero. $P(-x)=-24x^{3}+10x^{2}+13x-6$ has 2 sign changes, we expect 2 or 0 negative zeros. With synthetic division, we try the integers first. None of the integers are zeros. Try the fractions ... $\pm$1/2... \begin{array}{rrrrr} - 1/2\ \rceil & 24 & 10 & -13 & -6 \\ & & -12 & 1 & 6 \\ \hline & 24 & -2 & -12 & 0 \\ & & & & \\ - 2/3 \ \rceil & 24 & -2 & -12 & \\ & & -16 & 12 & \\ \hline & 24 & -18 & 0 & \\ & & & & \\ 3/4 \ \rceil & 24 & -18 & & \\ & & 18 & & \\ \hline & 24 & 0 & & \\ \end{array} Zeros:$\displaystyle \quad \frac{1}{2},\quad \frac{3}{4},\quad- \frac{2}{3}$ $P(x)=24(x-\displaystyle \frac{1}{2})(x-\frac{3}{4})(x+\frac{2}{3})$ $=2(x-\displaystyle \frac{1}{2})\cdot 4(x-\frac{3}{4})\cdot 3(x+\frac{2}{3})$ $=(2x-1)(4x-3)(3x+2)$
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