## Precalculus (6th Edition) Blitzer

small circle: $x^2+y^2=9$ large circle: $x^2+y^2=25$
Step 1. Using the figure in the exercise and given conditions, we have $a=5, b=3$, centered at $(0,0)$ for all curves. Step 2. For the small circle (green), we have $r=b=3$; thus the equation is $x^2+y^2=9$ Step 3. For the large circle (blue), we have $r=a=5$; thus the equation is $x^2+y^2=25$