Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 2: Limits and Continuity - Section 2.5 - Continuity - Exercises 2.5 - Page 85: 59

Answer

See the explanation below.

Work Step by Step

If we want $f$ to be discontinuous at 2, we make $f(2)$ undefined. The easiest way is to place $(x-2)$ in the denominator. We now define $f$ in such a way that it has a limit at x=2, by choosing a numerator that we can factor so it cancels the denominator. We do this if we want a removable discontinuity. For example, let the numerator = $x(x-2)=x^{2}-2x$. So, $f(x)=\displaystyle \frac{x^{2}-2x}{x-2},\ \displaystyle \quad\lim_{x\rightarrow 2}f(x)=\lim_{x\rightarrow 2}\frac{x(x-2)}{x-2}=\lim_{x\rightarrow 2}x=2$. The discontinuity can be removed by redefining $f$ $f(x)=\left\{\begin{array}{lll} \dfrac{x^{2}-2x}{x-2} & if & x\neq 2\\ 2 & if & x=2 \end{array}\right.$
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