Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 3 - The Derivative - Chapter Review - Review Exercises - Page 189: 44

Answer

$$ f(x)=\left\{\begin{array}{ll}{2} & {\text { if } \quad x \lt 0} \\ {-x^{2}+x+2} & {\text { if } \quad 0 \leq x \leq 2}\\ {1} & {\text { if }\quad x>2}\end{array}\right. $$ (a) graphed the function. (b) The graph is discontinuous at $x=2.$ (c) $$ \lim _{x \rightarrow 2^{-}} f(x)=\lim _{x \rightarrow 2^{-}}\left(-x^{2}+x+2 \right)=0 $$ From the right, where $x$-values are greater than 2, $$ \lim _{x \rightarrow 2^{+}} f(x)=\lim _{x \rightarrow 2^{+}}\left(1\right)=1 $$ so, $ \lim _{x \rightarrow 2} f(x) $ does not exist since $$ \lim _{x \rightarrow 2^{+}} f(x) \ne \lim _{x \rightarrow 2^{-}}f(x) $$

Work Step by Step

$$ f(x)=\left\{\begin{array}{ll}{2} & {\text { if } \quad x \lt 0} \\ {-x^{2}+x+2} & {\text { if } \quad 0 \leq x \leq 2}\\ {1} & {\text { if }\quad x>2}\end{array}\right. $$ (a) graphed the function. (b) The graph is discontinuous at $x=2.$ (c) Since each piece of this function is a polynomial, the only $x$-values where $f$ might be discontinuous here are 0 and 2. We investigate at $x=2$ first. From the left, where $x$-values are less than $2$, $$ \lim _{x \rightarrow 2^{-}} f(x)=\lim _{x \rightarrow 2^{-}}\left(-x^{2}+x+2 \right)=0 $$ From the right, where $x$-values are greater than 2, $$ \lim _{x \rightarrow 2^{+}} f(x)=\lim _{x \rightarrow 2^{+}}\left(1\right)=1 $$ so, $ \lim _{x \rightarrow 2} f(x) $ does not exist since $$ \lim _{x \rightarrow 2^{+}} f(x) \ne \lim _{x \rightarrow 2^{-}}f(x) $$ Now, we investigate at $x=0$ first. From the left, where $x$-values are less than $0$, $$ \lim _{x \rightarrow 0^{-}} f(x)=\lim _{x \rightarrow 0^{-}}\left(2 \right)=2 $$ From the right, where $x$-values are greater than 0, $$ \lim _{x \rightarrow 0^{+}} f(x)=\lim _{x \rightarrow 0^{+}}\left(-x^{2}+x+2 \right)=2 $$ then we have $$ f(0)=\lim _{x \rightarrow 0^{+}} f(x)=\lim _{x \rightarrow 0^{-}}f(x)=2 $$ The graph is continuous at $x=0$
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