Answer
$$z=\frac{1}{2}\ln({x^2+y^2})$$
Work Step by Step
By the definition of revolution about z-axis,
$$y\rightarrow \sqrt{y^2+x^2}$$
Substituting in $z=\ln{y}$, we get
$$z=\frac{1}{2}\ln({x^2+y^2})$$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.