College Algebra 7th Edition

Published by Brooks Cole
ISBN 10: 1305115546
ISBN 13: 978-1-30511-554-5

Chapter 3, Polynomial and Rational Functions - Section 3.4 - Real Zeros of Polynomials - 3.4 Exercises - Page 320: 51

Answer

$x\displaystyle \in\left\{ \frac{1- \sqrt {3}}{2}, \frac{1+ \sqrt {3}}{2},\frac{1}{2}\right\}$

Work Step by Step

See The Rational Zero Theorem: If $\frac{p}{q}$ is a zero of the polynomial $f(x) $with integer coefficients, then $p$ is a factor of the constant term, $a_{0}$, and $q$ is a factor of the leading coefficient, $a_{n}$. ------------------------ $f(x)=4x^{3}-6x^{2}+1$ Candidates for zeros, $\frac{p}{q}:$ $p:\qquad \pm 1,$ $q:\qquad \pm 1, \pm2, \pm4$ $\displaystyle \frac{p}{q}:\qquad \pm 1, \pm \frac{1}{2}, \pm \frac{1}{4}$ Try for $x=\frac{1}{2}:$ $\begin{array}{lllll} \underline{\frac{1}{2}}|& 4& -6 & 0 & 1\\ & & 2& -2& -1\\ & -- & -- & -- & --\\ & 4 & -4& -2 & |\underline{0} \end{array}$ $\frac{1}{2}$ is a zero, $f(x)=(x-\frac{1}{2})(4x^2-4x-2)$ Solving for the trinomial, using the quadratic formula for the quadratic equation of $ax^2+bx+c$, $x=\frac{-b\pm \sqrt {b^2-4ac}}{2a}$. in this case, $4^2-4x-2$, $x=\frac{4\pm \sqrt {-4^2-4 \times 4\times (-2)}}{2\times 4}=\frac{4\pm 4\sqrt {3}}{8}=\frac{1\pm\sqrt 3}{2}$. Therefore, the real zeros of the equations are: $x\displaystyle \in\left\{ \frac{1- \sqrt {3}}{2}, \frac{1+ \sqrt {3}}{2},\frac{1}{2}\right\}$
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