Let the coordinates of the fourth vertex D be (x, y).
We know that diagonals of a rhombus bisect each other.
∴ Midpoint of AC = Midpoint of BD …(i)
Coordinates of the midpoint of AC are
⇒ 2 + x = 3 and 7 + y = 7
⇒ x = 1 and y = 0
Thus, the coordinates of the vertex D are (1, 0)