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: 4

Answer

1. \(\displaystyle (G \circ F)(x) = x.\) 2. \(\displaystyle (F \circ G)(x) = x.\) 3. They are **equal** and both are the identity function on \(\mathbb{R}\).

Work Step by Step

**Step 1. Identify the given functions.** \(F(x) = x^5\). \(G(x) = x^{1/5}\). Both are defined for **all real** \(x\). (Because the 5th root function is well-defined for negative, zero, and positive inputs.) --- ## 1. Compute \(G \circ F\) \[ (G \circ F)(x) \;=\; G\bigl(F(x)\bigr) \;=\; G\bigl(x^5\bigr) \;=\; \bigl(x^5\bigr)^{1/5}. \] For real \(x\), since 5 is an **odd** exponent/root, \(\bigl(x^5\bigr)^{1/5} = x\). Thus, \[ (G \circ F)(x) = x. \] ## 2. Compute \(F \circ G\) \[ (F \circ G)(x) \;=\; F\bigl(G(x)\bigr) \;=\; F\bigl(x^{1/5}\bigr) \;=\; \bigl(x^{1/5}\bigr)^5. \] Again, because the exponent and root are both 5 (an odd integer), \(\bigl(x^{1/5}\bigr)^5 = x\) for all real \(x\). Hence, \[ (F \circ G)(x) = x. \] ## 3. Are \(G \circ F\) and \(F \circ G\) Equal? Yes. We have \[ (G \circ F)(x) \;=\; x \quad\text{and}\quad (F \circ G)(x) \;=\; x, \] so **for all real \(x\)**, \[ (G \circ F)(x) \;=\; (F \circ G)(x) \;=\; x. \]
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