## Thomas' Calculus 13th Edition

a. Domain : A set of all $(x,y)$ when $x \ne 0$ . b. Range: The range is $\dfrac{-\pi}{2} \leq z\leq \dfrac{\pi}{2}$ c. The level curves are the straight lines whose the form of $y=cx$ for any real number when $x \ne 0$. d. Boundary points refers to a straight line when $x=0$ e. Open f. Unbounded