Precalculus (6th Edition)

Published by Pearson
ISBN 10: 013421742X
ISBN 13: 978-0-13421-742-0

Chapter 3 - Polynomial and Rational Functions - 3.3 Zeros of Polynomial Functions - 3.3 Exercises - Page 337: 68

Answer

$$\color{blue}{ f(x)= x^4-7x^3+17x^2-x-26 }$$

Work Step by Step

We are given zeros and asked to write a polynomial function. If $3+2i $ is a zero, then $n +3+2i =0$ $n +2i = -3 $ $n= -3-2i $ So our factor is $\bf{(x -3-2i )}$ because when $x= 3+2i $, $(x -3-2i )=0$ Since $ 3+2i $ is a complex number, its conjugate, $ 3-2i $ is also a zero $n +3-2i =0$ $n-2i= -3 $ $n=-3+2i$ So our factor is $\bf{(x-3+2i)}$ because when $x= 3-2i $, $(x-3+2i )=0$ If $ -1 $ is a zero, then $n -1 =0$ $n = 1 $ So our factor is $\bf{(x +1 )}$ because when $x= -1 $, $(x +1 )=0$ If $ 2 $ is a zero, then $n +2 =0$ $n= -2 $ So our factor is $\bf{(x -2 )}$ because when $x=2 $, $(x -2 )=0$ So our function is: $f(x)=(x-3-2i)(x-3+2i)(x +1)(x-2)$ $f(x)=(x^2-6x+9-4i^2)(x +1)(x-2)$ Recall that $i^2=-1$ $f(x)=(x^2-6x+9-4(-1))(x +1)(x-2)$ $f(x)=(x^2-6x+13)(x +1)(x-2)$ $f(x)=(x^2-6x+13)(x +1)(x-2)$ $f(x)=(x^3-5x^2+7x+13)(x-2)$ $$\color{blue}{ f(x)= x^4-7x^3+17x^2-x-26 }$$
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