ones you know the coordinates of the given points A,B, and C, you can find slopes of the lines passing through AB and BC
then you find equations of the lines perpendicular to segments AB and BC ; recall these lines will have a slope negative reciprocal to the slopes of lines passing through segments AB and BC
ones you get slopes, use the coordinates of one point and point slope formula to find equations of the lines perpendicular to segments AB and BC
then find their intersection point which will be the center of the circle
after you find coordinates of a center, use distance formula to find the length of radius, multiply by 2 and you will get diameter
