#### Answer

True

#### Work Step by Step

Given: $f(x,y)=sinx+siny$
Take derivative.
$D_{u}(x,y)=cosx+cosy$
Since, $D_{u}(x,y) \leq |∇ f(x,y)| =|cosx+cosy|$
$=\sqrt {cos^{2}x+cos^{2}y}\leq \sqrt {1+1}=\sqrt 2$
Hence, the given statement is true.

Published by
Cengage

ISBN 10:
1285740629

ISBN 13:
978-1-28574-062-1

True

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