Circle Equation: A general equation for a circle in standard form is (x - h)^2 + (y - k)^2 = r^2, where (h,k) represents the center coordinates and r represents the radius.
Quadratic Equation: An equation involving x or y raised to the second power that can be written in standard form as ax^2 + bx + c = 0.
Pythagorean Theorem: The theorem states that in a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides. In this case, it applies because x^2 + y^2 is equal to the square of the radius.