Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 3 - Section 3.3 - Dividng Polynomials - 3.3 Exercises - Page 274: 70

Answer

$P(x)=2x^5+2x^4-18x^3-18x^2+40x+40$

Work Step by Step

RECALL: If c is a zero of a polynomial, then $x-c$ is a factor of the polynomial. Since -2, -1, 2, and $\sqrt5$ are zeros of the polynomial, and radical zeros always come in conjugate pairs, then $(x+2),(x+1), (x-2), (x-\sqrt5)$ and $(x+\sqrt5)$ are factors of the polynomial. Thus, the polynomial of degree 5 with the given zeros is: $\\P(x)=a(x+2)(x+1)(x-2)(x-\sqrt5)(x+\sqrt5) \\P(x)=a(x^5+x^4-9x^3-9x^2+20x+20)$ where $a$ is a real number. Since the constant term is 40, then $a$ must be: $\\a(20)=40 \\a=\frac{40}{20} \\a=2$ Thus, the polynomial with the given zeros whose constant term is 40 is: $\\P(x)=2(x^5+x^4-9x^3-9x^2+20x+20) \\P(x)=2x^5+2x^4-18x^3-18x^2+40x+40$
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