Here's a couple :
1. If the ends of a diameter are 11,-6) and (1,14) then the midpoint is the center of the circle
So we have that [ (11 + 1) / 2 , (14 - 6)/2 ] = [ 12/2, 8/2 ] = (6, 4) is the center
And the radius^2 can be computed as [ ( 1 -6)^2 + (14 -4)^2 ] = [ 5^2 + 10^2] = 125
So...the equation of the circle is
( x - 6)^2 + (y - 4)^2 =125
x^2 - 12x + 36 + y^2 - 8y + 16 = 125
x^2 + y^2 - 12x - 8y - 73 = 0
