Draw AE, DF parallel to x-axis
Draw BE, CF parallel to y-axis
In right triangles ΔAEB, ΔDFE
AB = DC
∠BAE = ∠CDF ∠ABE = ∠DCF
∴ AE = DF = x2 – x1
BE = CF = y2 – y1
x coordinate of C = x3 + DF = x3 + x2 -x,
y coordinate of C = y3 + CF = y3 + y2 – y
∴ C has the coordinates = (x2 + x3 – x1, y2 + y3 – y3)