Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 9 - Infinite Series - 9.2 Monotone Sequences - Exercises Set 9.2 - Page 613: 21

Answer

The sequence is eventually strictly increasing

Work Step by Step

Step 1. We're given the sequence \[ \{2n^2 - 7n\}_{n=1}^\infty \] and we're asked to show that the given sequence is strictly increasing or strictly decreasing. Step 2. Let \[ f(x) = 2x^2 - 7x \] so that the $n$th term in the given sequence is \[ a_n = f(n). \] Step 3. Let's find the first derivative, \[ f'(x). \] \[ f'(x) = 4x - 7 \] Hence, the function $f$ is increasing for $x > \frac{7}{4}$. Step 4. Thus, \[ a_n = f(n) < f(n+1) = a_{n+1} \] for $n \geq 2$, which proves that the given sequence is eventually strictly increasing. Result The given sequence is eventually strictly increasing.
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