AB is diameter of a circle with centre C.
Coordinates of C(2, -3) and other point is B (1, 4)
Point C is the midpoint of AB.
Let (x, y) be the coordinates of A, then
2 = (x+1)/2
4 = x +1
x = 3
and
-3 = (y+4)/2
-6 =y +4
or y = -10
So, coordinates of A are (3, -10).