Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 4 - Section 4.1 - Maximum and Minimum Values - 4.1 Exercises - Page 285: 77

Answer

The function $~~f(x) = x^{101}+x^{51}+x+1~~$ has neither a local maximum nor a local minimum.

Work Step by Step

Note that the function is continuous and differentiable for all real numbers. We can find the values of $x$ when $f'(x) = 0$: $f(x) = x^{101}+x^{51}+x+1$ $f'(x) = 101x^{100}+51x^{50}+1 = 0$ Let $y = x^{50}$. Then: $101x^{100}+51x^{50}+1 = 101y^2+51y+1 = 0$ We can use the quadratic formula to find the values of $y$: $y = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$ $y = \frac{-51 \pm \sqrt{(51)^2-4(101)(1)}}{(2)(101)}$ $y = \frac{-51 \pm \sqrt{2197}}{202}$ $y = -0.020435, -0.4845$ Since $y = x^{50}$, we can set up two equations: $x^{50} = -0.020435$ $x^{50} = -0.4845$ However, since $x^{50} \geq 0$ for all real numbers, these two equations have no solutions. Then there are no values of $x$ such that $f'(x) = 0$. Since the function is continuous and differentiable for all real numbers, the function has neither a local maximum nor a local minimum.
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