Algebraic Curve/Examples/Circle

Example of Algebraic Curve
The circle is an example of an algebraic curve.

From Cartesian Equation of Circle, a circle can be expressed by an equation in the form:
 * $\paren {x - a}^2 + \paren {y - b}^2 = R^2$

For example:
 * $x^2 + y^2 = 4$

is the equation defining a circle whose center is at $\tuple {0, 0}$ and whose radius is $2$.