SOLUTION: A circle passes through A and B, and its tangent to CD. Find its area, in cm^2. Diagram: https://imgur.com/a/XZgTPss

Draw a circle passing through A & B tangent to CD.   

Let 

 r be the radius 

 h the distance from the center O of the circle to the line AB

 M the midpoint of line AB



Then:

   (1)

and

  (2)    (from the triangle OAM)





Substitute (1) into (2) to eliminate h:





This simplifies to  r=5.2cm,  so the circle has an area of  approximately