Find the equation of a circle which is tangent to x-axis and whose center is at (4,2)

Hello:

an equation x-axis is y = 0

the ridus is the distance betwen the center and x-axis:

r = | (0) (4) + (1) (2) + 0 | / √ ((0) ² + (1) ²) = 2/1 = 2

an equation of the circle is : (x - 4) ² + (y-2) ² = 4