Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 14 - Section 14.2 - Limits and Continuity - 14.2 Exercise - Page 960: 4

Answer

The limit does not exist

Work Step by Step

Let's make the table: \[ \begin{array}{|c|c|c|c|} \hline \textbf{x\y} & \textbf{-0.05} & \textbf{0.05}& \textbf{0.1} \\ \hline \textbf{-0.05} & 0.6667 & -0.6667 & -0.5\\ \hline \textbf{0.05} & -0.6667 & 0.6667 & 0.5 \\ \hline \textbf{0.1} & -0.5 & 0.5 & 0.667\\ \hline \end{array} \] The function doesn't seem to have limit at origin. Let's consider the line $y=x$: $\lim_{(x, y)\rightarrow(0,0)}\frac{2xy}{x^2+2y^2}=\lim_{(x, x)\rightarrow(0,0)}\frac{2x^2}{x^2+2x^2}=\frac{2}{3}$ Now let's consider the line $y=-x$: $\lim_{(x, y)\rightarrow(0,0)}\frac{2xy}{x^2+2y^2}=\lim_{(x, -x)\rightarrow(0,0)}\frac{-2x^2}{x^2+2x^2}=-\frac{2}{3}$ As the limits are distinct, the function has no limit at the origin.
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