Center: In a circle, it is the point from which all the points in the circle are equidistant.

Circle: It is made of the set of all points in a plane laying at a constant distant r from a given point called center. If the radius is r and the center at (h,k) then the equation of the circle is given by  (x-h)² + (y-k)² = r²

Completing the Square: Method that finds the constant term in an incomplete perfect square trinomial of a second degree equation to solve it.

Conic section: A figure that is obtained slicing a double cone with a plane. (parabola, circle, hyperbola, and ellipse)

Factoring: The process to brake a polynomial down into the product of several factors.

Factors: All whole numbers that are multiplied together to yield another number.

Factored Form: Any polynomial that is written as the product of polynomials of lower degree that may be obtained from the original polynomial.

Radius: For a circle the radius is the segment with endpoints at the center of the circle and the circle.

Standard form of an equation of a circle: 

(x-h)² + (y-k)² = r² where (h,k) is the center and r is the radius.