Rigid Motion:
Any way of moving all the points in the plane such that
a) the relative distance between points stays the same and
b) the relative position of the points stays the same.
There are four types of rigid motions that we will consider: translation , rotation, reflection, and glide reflection.

In a translation, everything is moved by the same amount and in the same direction. Every translation has a direction and a distance.

A rotation fixes one point (the rotocenter) and everything rotates by the same amount around that point. Every rotation has a rotocenter and an angle.

A reflection fixes a mirror line in the plane and exchanges points from one side of the line with points on the other side of the mirror at the same distance from the mirror. Every reflection has a mirror line.

Glide Reflection:
A glide reflection is a mirror reflection followed by a translation parallel to the mirror. Every glide reflection has a mirror line and translation distance.

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