Chapter 10 - Parametric and Polar Curves - 10.2 Polar Coordinates - 10.2 Exercises - Page 729: 29

$$\eqalign{ & {x^2} + {y^2} = 4 \cr & {\text{The resulting curve is circle centered at the origin }} \cr & {\text{with radius 2}} \cr} $$

$$\eqalign{ & r = 2 \cr & {\text{Where }}r = \sqrt {{x^2} + {y^2}} \cr & \sqrt {{x^2} + {y^2}} = 2 \cr & {\text{Square both sides}} \cr & {x^2} + {y^2} = {\left( 2 \right)^2} \cr & {\text{The resulting curve is circle centered at the origin }} \cr & {\text{with radius 2}} \cr} $$