Let the third vertex of a triangle be (x, y)
Here, x1 = 2√3, x2 = 2√3, x3 = x
and y1 = -1, y2 = 5, y3 = y
and the coordinates of the centroid is (√3, 2)
We know that

⇒ 4√3 + x = 3√3 and 4 + y = 6
⇒ x = -√3 and y = 2
Hence, the third vertex of a triangle is (-√3, 2)