Each of Exercises $63-66$ gives a function $f(x, y, z)$ and a positive number $\epsilon .$ In each exercise, show that there exists a $\delta>0$ such that for all $(x, y, z)$ ,

$$

\quad \sqrt{x^{2}+y^{2}+z^{2}}<\delta \Rightarrow|f(x, y, z)-f(0,0,0)|<\epsilon

$$

$$

f(x, y, z)=\tan ^{2} x+\tan ^{2} y+\tan ^{2} z, \quad \epsilon=0.03

$$