## Thomas' Calculus 13th Edition

$1$
Here, $\lim\limits_{(x,y) \to (0,\dfrac{\pi}{4})} \sec x \tan y=\sec(0) \tan (\dfrac{\pi}{4})$ Thus, $\lim\limits_{(x,y) \to (0,\dfrac{\pi}{4})} \sec x \tan y=(1)(1)=1$