Discrete Mathematics with Applications 4th Edition

Published by Cengage Learning
ISBN 10: 0-49539-132-8
ISBN 13: 978-0-49539-132-6

Chapter 7 - Functions - Exercise Set 7.3 - Page 426: 3

Answer

1. \(\displaystyle (G \circ F)(x) = x^3 - 1.\) 2. \(\displaystyle (F \circ G)(x) = (x - 1)^3 = x^3 - 3x^2 + 3x - 1.\) 3. They are **not equal** as functions on \(\mathbb{R}\).

Work Step by Step

**Step 1. Identify the given functions.** - \(F(x) = x^3\). - \(G(x) = x - 1\). Both are defined for all real \(x\). --- ## 1. Compute \(G \circ F\) \[ (G \circ F)(x) \;=\; G\bigl(F(x)\bigr) \;=\; G\bigl(x^3\bigr) \;=\; x^3 \;-\; 1. \] --- ## 2. Compute \(F \circ G\) \[ (F \circ G)(x) \;=\; F\bigl(G(x)\bigr) \;=\; F\bigl(x - 1\bigr) \;=\; (\,x - 1\,)^3 \;=\; x^3 \;-\; 3x^2 \;+\; 3x \;-\; 1. \] --- ## 3. Are \(G \circ F\) and \(F \circ G\) Equal? - We have \[ (G \circ F)(x) \;=\; x^3 - 1 \quad\text{and}\quad (F \circ G)(x) \;=\; x^3 - 3x^2 + 3x - 1. \] - Compare the two expressions: \[ x^3 - 1 \quad\text{vs.}\quad x^3 - 3x^2 + 3x - 1. \] Clearly, these are **not** the same polynomial unless \( -3x^2 + 3x = 0\), which only happens for specific \(x\) values (namely \(x=0\) or \(x=1\)). Hence, for general \(x\in\mathbb{R}\), \[ (G \circ F)(x) \;\neq\; (F \circ G)(x). \]
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