## 7. Translations.

Given in
a prefixed
vector **τ***(α ; β)*, if we add this vector to every point
P*(x;y)* of a polygon Π we obtain a polygon Π' in which every point
P'*(x+α;y+β)* corresponds to Π in a bijective way.

The sides of Π' are equal and parallel to the
corresponding sides of Π, so that the corresponding angles are equal and the two
figures are congruent.

Such transformations of Π into Π' are said translations.

A translation is an isometry.