Precalculus (10th Edition)

Published by Pearson
ISBN 10: 0-32197-907-9
ISBN 13: 978-0-32197-907-0

Chapter 4 - Polynomial and Rational Functions - 4.6 Complex Zeros; Fundamental Theorem of Algebra - 4.6 Assess Your Understanding - Page 240: 22

Answer

$f(x)=x^5-5x^4+11x^3-13x^2+8x-2.$

Work Step by Step

The Conjugate Pairs Theorem says that if a polynomial has real coefficients, then any complex zeros occur in conjugate pairs. That is, if $a + bi$ is a zero then so is $a – bi$ and vice-versa. Therefore the zeros of the function are: $1\pm i$ and $1$ with multiplicity $3$. Hence the function could e.g. be: $(x-(1+i))(x-(1-i))(x-1)(x-1)(x-1)\\=(x-1-i)(x-1+i)(x-1)^3\\=((x-1)^2-i^2)(x^3 - 3 x^2 + 3 x - 1)\\=(x^2-2x+1+1)(x^3 - 3 x^2 + 3 x - 1)\\=(x^2-2x+2)(x^3 - 3 x^2 + 3 x - 1)\\=x^5-5x^4+11x^3-13x^2+8x-2.$
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