(Solved): Find the center-radius form of the equation of the circle with center (4,9) and tangent to the x-a ...

Find the center-radius form of the equation of the circle with center $$(4,9)$$ and tangent to the x-axis. (Hint: A line tangent to a circle touches it at exactly one point.) Type the center-radius form of the equation of the circle. (Type an equation. Simplify your answer.)