In order to determine the coordinates of ABCD, it is necessary to apply the following transformation to figure A'B'C'D':
r(-90°,0)(A'B'C'D')
or, which is equivalent, apply a clockwise rotation of 90°, which is represented as follow:
T(x,y) => (y,-x)
then, for the points A', B', C' and D', you obtain:
A'(2,1) => A(1,-2)
B'(-4,-2) => B(-2,4)
C'(-4,-6) => C(-6,4)
D'(-1,-3) => D(-3,1)
