The Decatur Police Department said on Jan. 29 around 10:30 p.m., Morgan County 911 received a call of a vehicle on fire on Point Mallard Circle and Greenwood Drive southeast. Sully Sullenberger ...

You are usually given the point - it's where the tangent meets the circle. To find the gradient use the fact that the tangent is perpendicular to the radius from the point it meets the circle.