Since A(x, y) is the point of equidistance between B and C, then
AB = AC
(AB)2 = (AC)2
Using the distance formula,
(x - 0)2 + (y - 2)2 = (x - 2)2 + (y - 1)2
x2 + y2 - 4y + 4 = x2 - 4x + 4 + y2 - 2y + 1
x2 - x2 + y2 - y2 + 4x - 4y + 2y = 5 - 4
4x - 2y = 1
