Calculus 10th Edition

Published by Brooks Cole
ISBN 10: 1-28505-709-0
ISBN 13: 978-1-28505-709-5

Chapter 13 - Functions of Several Variables - 13.2 Exercises - Page 887: 17

Answer

The limit is $$\lim_{(x,y)\to(\pi/4,2)}y\cos xy=\boxed{0}.$$ The function is continuous on its domain.

Work Step by Step

We will calculate this limit by simple substitution: $$\lim_{(x,y)\to(\pi/4,2)}y\cos xy = 2\cos\left(\frac{\pi}{4}\cdot2\right) = 2\cos\frac{\pi}{2}= 2\cdot0=0.$$ This function is continuous in every point because at every ordered pair $(x_0,y_0)$ just by substitution we have $$\lim_{(x,y)\to(x_0,y_0)}y\cos xy=y_0\cos x_0y_0.$$
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