When we rotate a geometrical shape by certain angle , the two preimage and Image are congruent, that is, neither the length of corresponding sides,nor Interior angles,as well as Area of two polygons does not change.
Claim Of Tessa
A rotation of 90° clockwise about the center of some polygons will carry the polygon onto itself.
The two Polygons are
1. Square----All four sides equal and all interior angle equal to 90 degree.
2. Equilateral Triangle=All three sides equal and all interior angles equal to 60 degree.