Chapter 2 - Section 2.5 - Equations of Lines and Linear Models - Summary Exercises on Graphs, Circles, Functions, and Equations - Page 231: 12

$x^2+(y-2)^2=4$ See graph.

A circle has the form: $(x-h)^2+(y-k)^2=r^2$ with center $(h,k)$ and radius $r$ Our center is $(0,2)$. Since the circle is tangent to the $x$-axis, the radius must be $2$ (vertical distance from x-axis to the center). So we have: $(x-0)^2+(y-2)^2=2^2=4$ $x^2+(y-2)^2=4$