Calculus: Early Transcendentals 8th Edition

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

Chapter 4 - Section 4.5 - Summary of Curve Sketching - 4.5 Exercises - Page 321: 11

Answer

A. The domain is $(-\infty,1)\cup (1,2)\cup (2, \infty)$ B. The y-intercept is $0$ The x-intercept is $0$ C. The function is not an even function or an odd function. D. $\lim\limits_{x \to -\infty} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to -\infty} \frac{-x}{x-2} = -1$ $\lim\limits_{x \to \infty} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to \infty} \frac{-x}{x-2} = -1$ $y = -1$ is a horizontal asymptote. $\lim\limits_{x \to 2^-} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to 2^-} \frac{-x}{x-2} = \infty$ $\lim\limits_{x \to 2^+} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to 2^+} \frac{-x}{x-2} = -\infty$ $x = 2$ is a vertical asymptote. E. The function is increasing on the intervals $(-\infty, 1)\cup (1,2)\cup (2, \infty)$ F. There is no local maximum or local minimum. G. The graph is concave down on the interval $(2,\infty)$ The graph is concave up on the intervals $(-\infty,1)\cup (1,2)$ There are no points of inflection. H. We can see a sketch of the curve below.

Work Step by Step

$y = \frac{x-x^2}{2-3x+x^2} = \frac{x(1-x)}{(x-2)(x-1)} = \frac{-x}{x-2},~~~x \neq 1$ A. The function is defined for all real numbers except $x=1$ and $x=2$ The domain is $(-\infty,1)\cup (1,2)\cup (2, \infty)$ B. When $x = 0$, then $y = \frac{0-0^2}{2-3(0)+0^2}= 0$ The y-intercept is $0$ When $y = 0$: $\frac{x-x^2}{2-3x+x^2} = 0$ $x(1-x) = 0$ $x = 0$ Note that $x\neq 1$ The x-intercept is $0$ C. The function is not an even function or an odd function. D. $\lim\limits_{x \to -\infty} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to -\infty} \frac{-x}{x-2} = -1$ $\lim\limits_{x \to \infty} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to \infty} \frac{-x}{x-2} = -1$ $y = -1$ is a horizontal asymptote. $\lim\limits_{x \to 2^-} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to 2^-} \frac{-x}{x-2} = \infty$ $\lim\limits_{x \to 2^+} \frac{x-x^2}{2-3x+x^2} = \lim\limits_{x \to 2^+} \frac{-x}{x-2} = -\infty$ $x = 2$ is a vertical asymptote. E. We can try to find the values of $x$ such that $y' = 0$: $y' = \frac{(-1)(x-2)-(-x)(1)}{(x-2)^2} = \frac{2}{(x-2)^2}$ There are no values of $x$ such that $y' = 0$ When $x \lt 1$ or $1 \lt x \lt 2$ or $x \gt 2$, then $y' \gt 0$ The function is increasing on the intervals $(-\infty, 1)\cup (1,2)\cup (2, \infty)$ F. There is no local maximum or local minimum since the graph is increasing on all intervals. G. We can try to find the values of $x$ such that $y'' = 0$: $y'' =\frac{-(2)(2)(x-2)}{(x-2)^4} = \frac{-4}{(x-2)^3}$ There are no values of $x$ such that $y'' = 0$ When $x \gt 2$ then $y'' \lt 0$ The graph is concave down on the interval $(2,\infty)$ When $x \lt 1$ or $1 \lt x \lt 2$, then $y'' \gt 0$ The graph is concave up on the intervals $(-\infty,1)\cup (1,2)$ There are no points of inflection. H. We can see a sketch of the curve below.
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