Answer :
Changes in a coordinate [tex](x,\ y)[/tex] can be observed with 90 degree rotations about the origin.
90 degrees CW = [tex](y,\ -x)[/tex]
180 degrees CW = [tex](-x,\ -y)[/tex]
270 degrees CW = [tex](-y,\ x)[/tex]
Let's observe M(10, 12) and M'(12, -10).
Since they switched and the x value became negative, it must have been a 90 degree rotation.
90 degrees CW = [tex](y,\ -x)[/tex]
180 degrees CW = [tex](-x,\ -y)[/tex]
270 degrees CW = [tex](-y,\ x)[/tex]
Let's observe M(10, 12) and M'(12, -10).
Since they switched and the x value became negative, it must have been a 90 degree rotation.