Given three concentric (having the same center) circles.
Their radii are 1,2 and 3.
Place three points A,B,C  each on a different circle to get a triangle ABC
with a maximal area.
What is this area?
(In reply to
Another approach (spoiler) by Harry)
my solution has a slight mistake. To compute the area of the triangle I used the coordinate matrix formula and in doing so forgot the 1/2 times the determinant and thus the reason why my area is twice yours.

Posted by Daniel
on 20100911 22:37:01 