Rotation and congruence

Congruence comes from a latin word  congruere  which means "  to agree ". So the shapes agree .

The following shapes are congruent, because although they are oriented and coloured differently we can place one on top of the other so that the two coincide exactly (i.e., they are the same shape and size). In order to see this, we need to pick up one of the pieces, flip it over (reflect it), and turn it (rotate it)