The centroid of a non-equilateral triangle divides the line orthocenter and circumcentre in 2:1, thus, the coordinates of circumcentre is (h, k), then (
2+5
3
,
2k+8
3
)=(3,
14
3
) (h,k)=(2,3) The image of orthocenter (5, 8) with respect to side BC, So, the radius of circumcircle of ∆ABC is √(8−2)2+(5−3)2=√40=2√10 So, the diameter is 4√10.