__Matched Exercise 1:__ Find the equation of a
circle whose center is at (2 , - 4) and radius 3.

__Solution to Matched Exercise 1:__

(x - 2)^{2} + (y + 4)^{2} = 9

__Matched Exercise 2:__ Find the equation of a
circle that has a diameter with the endpoints given by A(0 , -2) and B(0 , 2).

__Solution to Matched Exercise 2:__

center at (0 , 0)

radius = 2

equation: x^{2} + y^{2} = 4

__Matched Exercise 3:__ Find the center
and radius of the circle with equation

x^{2} - 2x + y^{2} - 8y + 1 = 0

__Solution to Matched Exercise 3:__

write the given equation in standard form by completing the squares.

(x - 1)^{2} + (y - 4)^{2} = 4^{2}

radius = 4

center at (1 , 4).