Standard form of circle is , where is center and  is the radius.

The circle center .

The circle is tangent to the line means the circle meets the line at only one point .

The -coordinate of the point is .

Since the center is , the point on the circle must be .

The distance between and is radius of the circle.

Radius of the circle is .

Substitute the values and in .

.

The circle equation in standard form is .